I have a 1990 with 5,000 miles. Just recently, the bike has been shifting weird. It will down shift just fine but when I up shift it only shifts partly. I'll go from first to second (finding neutral sometimes by accident) and it will engage but I don't hear or feel it and then WHAM it will pop out of second and go into neutral. I took off my right side cover and watched the lever and springs while I shifted it and I could see it not fully engaging. As far as I can tell there are no adjustments on this part. Any thoughts?