Case in point:





The spaces between the letters narrows down to about 1mm on my ZX. ZRX had the same problem, but I removed the letters on that gastank. Not going to do that on the ZX as it's 27 years old & 100% original/stock... plus they're a royal PITA to put back on.
Dental teeth polishing kit like this maybe?
Amazon.com

I tried foam swabs today with some Griots goop, but that just made a mess.