Need to change shift return spring on 1994Moto Guzzi 1100i. How do I do it?

You have spent alot of money on this. To no avail, have you had this on a dyno check the runningwith diagnostics

If you are good with wrenches and screwdrivers, yes you can, there are loads of parts for your bike out there. Get a book, get the clutch parts, get it ready for spring.

If synthetic lubricants deteriorate the plastic bearing housing, conventional lubricants will also deteriorate it. Use whatever lubricant you want of the proper type and viscosity. There is no "best" fluid. If unsure, or unwilling to do the research yourself, follow the manufacturer's suggestions.

Sounds like a slightly bent shift fork. But start with a oil and oil filter change. Dirt and grit in the oil can cause the same problem. If the problem gets worst you will need to replace the bad fork. This is a very involved project and bets done in the shop.

Please rate this solution. Thanks Fran :)

sounds as though your gear lever return spring has broken and will need replaceing