I have a Moog Opus 3 keyboard I aquired years ago and have pulled it out recently to use in some home recording. Still works but needs a good cleaning. I'm curious how old my unit is-what year it came out. The model number is 339A. If anyone has an idea that'd be great. Also looking for tips on cleaning this internally. Should I use compressed air or some type of contact cleaner? Any replies appreciated. Thanks Pj