The GS500 uses 29.5mm valve shims.  I pulled my GS apart and some of the shims in there were 29mm, obviously done by a previous owner. 

Apparently the 29.5mm shim is pretty rare and used only on a few Suzuki bikes.  This makes them harder to come by.  29mm shims however, are common on Yamahas, BMWs and others.

2 local bike shops I contacted had never heard of a 29.5mm shim.  One of them managed to dig up a shim kit of 29.5 shims... BUT many of them were actually 29mm that a tech had mistakenly mixed in there.  Yamaha marks many of their shims with a "Y"

In summary, next time you adjust valves, measure the diameter of the shims on your bike before reinstalling them, and also doublecheck any shims you buy that aren't in original packaging!

I'm not sure what damage it could cause, but the wear on the shim indicates it was slopping back and forth in there against the bucket and not rotating as it should.  Best case it'll make some extra noise, worst case it will wear out the cam/bucket/shim faster. 

Oldie but goodie.
GSTwin valve kit - make sure its the right ones - whoever has them kits.
Cool.
Buddha.

no one has a east coast kit that i know of it came up missing and i dont think one is goin to get put back on the market.  go figure i need it now...lol