I've done all the same things
pjleo said. With multiple RS's. I even sent one back to have it reconditioned, where I think they basically put a new wood casing over the old piezo so I could start over. It's all exactly as he said.
I prefer the sound of the p/u flipped over on my bass too w/ the "R" symbol facing the bass. But it does get a very lively sound the other way. A bit too bright and stringy on my bass.
Does using a shim change or degrade the sound? I've read differing opinions. I use a shim w/ a Planet Wing p/u and to my ears yes it does make a difference I can detect depending on which side of the p/u I place the shim.
Another option if you just need a slight adjustment is to wrap the p/u in Scotch tape as many times as needed to add just the right thickness. Cheap. Adjustable.
