How many rounds per year on the average went through that 500 over 30 years?
By "failing to lock into battery half the time" do you mean the bolt lock up on the barrel?
If so, chances are the locking lug and locking lug recess on the barrel extension are worn beyond the point of being serviceable.
A new bolt or at least a new locking lug and a new barrel should solve that problem.
Remington locking lugs are more oval shaped - not a square shaped lock up like the Mossberg's
When the Remington wears - the lock up starts to rattle and slosh around after about 100,000 to
150,000 rounds. The Mossbergs typically start doing this after 5,000 to 10,000 rounds depending upon what kind of ammo is used and how long the shooting sessions are.
What Remington did was offer an oversize locking lug with an "L" etched onto the lug. This takes up
the space in the worn locking lug recess in the barrel and extends the gun's life another 50,000 rounds by which time the barrel extension itself will likely develop a hairline crack near the end of the recess.
There's no official "lifetime" for these bolts and barrels - but I have been shooting trap for 25 years with Remingtons (1100 and 870) and have observed the barrels last about 150,000 - 250,000 rounds. The receivers possibly LESS since the rails wear down faster and the brazed on magazine tubes break off after - in my case 17 years of 10,000+ rounds per year.
Hall of Famer Rudy Etchen put a qtr million at least - through one 870 and I know of an 1100 that went about 200,000 rounds through a 1963 - first year production barrel
The Remington 870s and 1100s are more durable than Mossbergs over the long haul - just as you've revealed with your thread (although I have been "flamed" before for saying that on other shotgun threads) for continuous firing over long periods of time.
Nothing wrong with the Mossbergs - they're fine for what they were intended for. I have two 500s and two Rem. 870s