The Browning BPS ....I think is an equivalent gun in terms of quality to the Rem 870 Wingmaster...
and on my BPS 12ga Hunter model ...I started to see some wear on internal parts in the gun ( on the bolt traveler, a little bit on the action bars, etc.. about 15 yrs after I first bought that gun ....and in those days, it was my primary gun for Trap and bird hunting ...so about 15,000 shells a yr thru that gun ...so I'd call it about 225,000 shells at that point.
I still have that gun ....and its not a primary clay target gun anymore ...and the wear on it has not significantly increased...in the last 15 yrs...and I'd say it has about 250,000 shells thru it now.
Completely worn out as you observed...has to be at least 500,000 shells in my opinion - but who really knows...??
Wear on a pump gun ...or a semi-auto ....will always be greater than on an O/U ...where I know I have close to 250,000 shells thru some of my O/U's with very little, if any, wear on internal components.
Some of my grandpa's pump guns / semi-autos ..( bought in the 1920's - 1950's ....looked heavily used / in and out of gun racks in trucks, blinds, etc....and he killed a lot of game with it ...but I don't think he ever shot more than 250 shells a yr ...thru any of those guns .....where 40 yrs of use would only make up 10,000 shells..../ but a serious clay target shooter in that same time frame of the 30's - 50's ...put a lot of shells thru their guns just like many of us do today.
A gun made in 1963 ...isn't that old ...
--- especially compared to old guys like Klawman and Zippy..../ but if it did see 10,000 shells a yr...( 400 boxes a yr ) ... / that's almost 500,000 ...
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It might cost you more to repair that gun ...than its worth ...unless it has a lot of sentimental value to you ....it might just be better to sell it off for parts to someone ...and pick up something else to shoot ( I know you have other guns ...) .. / and I don't know what the new Wingmasters cost these days ...but the Browning BPS Hunter model, 12ga or 20ga, 28" barrel and Invector Plus chokes ..sells new for around $ 550 .... even though the list for about $ 659 ( and they come in 16ga, and 28ga and .410 as well ) but so does the Rem 870 Wingmaster I presume.../ not trying to talk you out of another Wingmaster...just using BPS as an example of the same quality - in my view.
http://www.browning.com/products/catalog/firearms/detail.asp?fid=011B&cid=012&tid=211&bg=x