I just got done cleaning my slider controls on my BM 3000-2.I first used a liberal amount of contact cleaner followed by a lubricating de-oxidizer type.They are are now noise free and operating well except not very smooth sliding.Is there some sort of grease that should be in there,possibly they should be dissassembled to get them working a bit smoother?Also the clear part of the slide rules have turned a bit yellow.Is this common due to age?Or is it normal?Are replacements available?