I have a marlin take down model 39 love the gun but my son starting hunting, amazing put down his 10/22 for my level and while shooting firing pin broke, not bad for 50yrs of use! GNP had a old model replacement, but when I got it it isn't exact at all, stuck way out the back of the receiver, had to file, grind, and polish, now it fits and works but every now and again the level  locks up, I try to work the level sometimes one to 5 tries then fine again??? I have looked at it again and can't figure it out....any suggestions.

Buy the correct firing pin that fits right.
The firing pin fit is critical in the Marlin's because the firing pin also is part of the bolt retraction system.
Here's a Marlin firing pin ID page:

http://www.wisnersinc.com/additional_info/Marlin22leverFP.html

They apparenlty make new ones in-house.

If they don't have the correct pin try Jack First.
Jack First is a top parts house and they also make some new parts to replace older, hard to find parts.
Give them a try:

http://www.jackfirstgun.com/

Thank you much for the info I'll try them.

Thank You, contacted Wisnerinc got the correct firing pin after some filing and fitting its in and working.
Jim