I switched from downtube shifters to a stem shifter on my Matsuri. Took it to my LBS for adjustment of the shifters. Bad news! Even though I sorta toyed around with shifter before installing it, the rear deraileur wont hold. It keeps slipping. Has anyone overhauled a stem shifter. It has click stops when going from the big cogs to the small cogs, but the click stops aren't strong enough to hold the gear. It worked fine with the down tube shifter. Am I ebay bound to find a working shifter?