Adcom 535L upgrades?

I have an old Adcom 535L amp (60wpc) from the 1990s. It's a utility amp and actually sounds decent if a bit grainy in the mids and highs. I'm not going to try to sell it, as it doesn't promise much on the used market. 

I'm wondering if anyone has replaced caps or other key parts in their older Adcom gear and if so whether (a) it made a real difference and (b) how much it cost? 

I have looked inside. Looks fine. Works fine. I'm in the Tweak-light Zone on this one, for sure!
The 535i is a well designed amplifier and responds well to upgrades. Do a search and you'll find a good bit of information about upgrade paths. If I remember correctly it was a Nelson Pass design. 
Here's one:
There was an outfit that specialized in upgrading 535i but I'm not sure if there are sill in business. Worth checking.  
I’ve owned a few 535s and they always worked flawlessly and sounded fine. I currently use a later 5300 as a backup/satellite (outdoor speakers) amp and sold the last of my 535s a few years ago. The 5300 is 85wpc and in my humble (!) opinion it sounds far better than a 535, even the later models (5 way binding posts added instead of the twisty things they had originally). I may get the 5300 upgraded someday or fixed if the caps get leaky as it just works as it should. Great torroidal/mosfet amps costing very little relative to how they sound.
Musical Concepts/Musical Design may be a rebuild or upgrade path as well. They are not cheap but their work is top shelf.