My 2007 T100 sometimes doesn`t want to downshift. The gear shifter feels like it`s not connected to anything. After a couple of trys it will work normal, doesn`t do all the time. I`m thinking the shift shaft might be getting worn. How involved is it to replace ? I`m a retired auto tech so not new to turning wrenches . I got a manual on the way. Any info would be helpful.