Hi Richard,
I've had trouble with scratchy pots on my Tributes, and microphonic pickups on my USA S-500.
First the Tributes. Craig is right, the Tributes do not use the larger (and better), imperial sized USA pots. Smaller, metric mini-pots are used instead. I had real trouble finding replacements of the right size but ended up buying some Mighty Mite mini-pots on E-Bay. They have been fine. I've also seen Alpha brand pots of the right size being sold on E-Bay.
Now the S-500 pickups. When I bought my S-500 third hand the neck pickup wasn't working and the other pickups made a loud 'clunk' when you moved the pickup selector switch or tapped the pick guard. I sent the neck pickup away to a luthier to get fixed and took the other 2 pickups out to see what the problem might be. I also did some Google-ing and found that microphonic MFD pickups are pretty common. On closer inspection of my MFD's I can see why. The whole pickup is held together at the bottom by a large ceramic bar magnet that runs the length of the pickup. It is held in place by a couple of dabs of glue and not much else. The glue had become brittle and was no longer attached to anything on my pickups, so the big bar magnet was free to respond to vibration and go microphonic. I put some new epoxy glue on the bar magnet and the microphonics were cured.
In the meantime, the luthier e-mailed me back to say he'd re-wound the broken neck pickup and it now worked. He also commented that the bar magnet was loose and the pickups really should have been wax potted to make them robust. Did I want him to wax pot the pickup? Darn right I did. So I had the neck pickup wax potted and I must say it is the nicest (and quietest) pickup of the 3 in my S-500.
IMHO the MFD pickups could be constructed a little better than they are, and comprehensive wax potting is a must.
I got my hands on some Legacy pickups to install while the MFD's were out of action and they are a NICE, well constructed pickup, right down to the vintage cloth covered wiring. I can't see why the MFD's aren't built to the same standard?
If your guitar is still under warranty get everything fixed by your dealer and save some euros.