Heya Caix,
Sweet Axe! Welcome aboard -
I hear ya bout not digging the rust esp on the pu pole pieces and bridge posts.... not a lot you can do bout it tho - that stuff never sleeps
It appears the previous owner(s) had some pretty gnarly hand sweat and/or never bothered to wipe down the guitar after playing it.
SOme of it is just normal wear & tear that comes with age - I've owned a couple 80's G&L's with DF bridges and both had rust on the bass side bridge post bolts - but the majority of it is no doubt due to said acidic sweat...
I'm a fan of naturally weathered & knack'd axes so I'm most likely not gonna be alot of help... IMO, I would (for the most part) leave it alone. Replace the parts that don't function due to the rust and look into replacement part rather then refinish them - there is a guy on this site & Ebay who offers replacement Leo-era spec p/gs - and check Ebay for original issue parts. No disrepect to G&L but they're in the business of making new guitars - and being a small company, its not cost effective for them to keep up with manufacturing parts for old(er) models.
It may take awhile & alot of $, but conceivably you could get all the parts (including another set of early S-500 pu's) and have what you want but I think you have an uphiil battle ahead of you if you go this route.
I remember Dan Erewine had a column in GP that dealt with restoring vintage guitars and reviving old parts... I believe he's written a book as well...
One other thing to keep in mind, speaking of vintage guitars - Leo-era G&L's, esp early models are increasing in value and while it may not be apparent to alot of folks now, they are in essence, vintage guitars (made by the Man himself). So, in my eyes, they will continue to increase in value - good idea to keep the stock parts you replace in case (Ha) you decide to sell the guitar down the road.
I guess it comes down to that - if you can't live with the guitar as it sits, then perhaps sell it and look for a cleaner example...
Personally, I'd clean it up a bit and enjoy it.
My .02 -
Cheers,
Kf