got a classic question for the hive. a good friend has a Smith & Wesson he doesn`t want. its a nickle model 39-2 with a serial # A618XXX. it has not been lovingly cared for. the mag is rusty, the whole thing is dirty and gummy and about a quarter of the nickle is peeling on the frame. I think the frame is aluminum cause a magnet will not attract it. slide is of course steel. rear sight is drift adjustable, not micro. the single action trigger break is surprisingly crisp with a very short reset, not bad at all.
he is a rather small man and is going thru a rough time that lots of us have, so money is short. he likes my Shields and hopes to get enough to get one in 9mm.
I have no experience with the older models and had to look on YT to find disassembly.
appreciate any advice here as Gunbroker and Google were really not much help.

Based on condition, not much.  39's have been creeping up in recent years, and nickels usually command a premium.  But with a quarter of the nickel gone, someone is probably looking at a refinish.  The other issue to consider is the internal condition.  If the outside is as bad as described, there may well be issues inside and these things are not easy to do a full break down on.  

My interest level would start at $200.  For a friend in need I might go $300 but it would have to be a very good friend.  Any one who buys this is probably going to have to throw money at it.

The value of the S&W 39-2 will be impacted in a negative way because S&W no longer support these pistols.   I bought a S&W 439 blued pistol off GB a couple years ago.  The finish was very poor but the pistol had not been shot very much but carried a lot.  I paid $265 IIRC and I suspect your nickel 39-2 in the condition you state with one mag would be $250 or less.   Mags and other accessories are getting more scarse and I would not use a 39-2 for self defense where the pistol would be shot on a regular basis.   If the pistol breaks it might take a while to get it repaired and there are better options today.

The S&W 39-2 is an updated version of the original model 39.  The primary change was to the extractor but these pistols were designed to feed FMJ ball ammo.  Most Model 39-2 pistols will function with hollow points and accuracy varies between different examples.  Some 39-2's can be very accurate but most have comparable accuracy to a Colt Commander.  The accuracy is completely acceptable for defense but may not put all rounds in the 10 ring from 25-50 yards.

The S&W 39-2 does not incorporate a firing pin safety (drop safety).  If you drop a 39-2 with a round in the chamber and the slide safety off (in fire mode) the round can fire from inertia.  If the slide safety is engaged with a round in the chamber and the pistol is dropped on the muzzle it should not fire.  The magazines hold eight rounds and I carried mine 8 + 1 in the chamber with two spare mags.  The S&W 39,39-2,439 & 6904/5904 incorporate a magazine safety.  The frame is aluminum alloy and generally robust and not known to frequently crack like Colt Commander 45's of that period.  The most common failures/breakage are extractors, slide stop wear/breakage and safety catch after extensive use.  My 39-2 hammer went bad and had to be replaced.

The 39-2 grip is comfortable for most users and the pistol displays moderate recoil for most shooters.  The Illinois State Police was the first Agency of any size to adopt the model 39 in 1968.  S&W released the 39-2 after consultation with the ISP as a product improvement.  It was through the ISP that S&W developed and released the 439 ( second generation) and the 5904 (third generation).

When the ISP first adopted the 39 they used full metal jacket ball ammunition.  The ISP tried to improve terminal ballistics by adopting a more rounded nose 100 grain FMJ (I actually have a box with a couple cartridges).   Then Govenor Walker's administation supposedly would not authorize hollow point ammunition so the ISP issued a 95 grain JSP and later a few WW 95 grain JSP.  When Governor Thompson took office he authorized the ISP to issue 9 MM JHP.   After failures associated with the first aluminum jacket Silvertips the ISP issued Federal 115 grain JHP 9PB.  ISP eventually adopted +P and finally Winchester Ranger 115 grain JHP +P+.  The original 39's & 39-2 functioned with the stubby 95 grain JSP after the armorers polished feed ramps and tweaked the chamber openings.  When I was issued the JHP ammunition I never encountered any feed issues with 439 or 5904.  I carried my 39-2 with 115 grain JHP and it was also reliable.

The S&W 39-2 and model 59 were very serviceable pistols and required less service from armorers than typical Colt and S&W revolvers which were more commonly carried by LE.   I started carrying a model 39-2 in 1975 where Deputies were authorized to carry S&W 39 or 59 pistols but the majority of Deputies and LE still carried revolvers.

Sorry I got long winded but I still enjoy shooting my S&W 9's and I appreciate the role they played in history.

well fellas, the two of you have provided more info that I thought I would get. thanks, seems like no matter the subject, somebody in the hive knows a lot.
I will clean, oil and function fire the gun and tell my pal its worth somewhere around $200.

A 39-2 in good condition is worth $350-$450. I paid $400 for mine and consider it money well spent.

Nickel is the wild card. Not everybody like nickel (I don't). Also, condition is everything so factor that accordingly. If the nickel is peeling, probably $250 tops.

Considering these pistols are pretty rugged it would not worry me about S&W factory unsupported. Plenty of spare parts out there not that you are likely to ever need one. Clean her up and leave the rough finish as is for a spare beater. No sense in refinishing.