Anyone that rebuilds these transmissions can tell you it takes about 10 seconds to look at a bearing and know the owner used any of the "synchro" oils. If your transmission doesn't shift smooth, rebuild it. By using a band aid such as synchroshift, you are hiding the real problem, and causing more issuse down the road.
Synchros need friction to work, bearings and gear teeth need good lubrication. By using a synchro shift type oil, you are increasing the friction in the transmission. It can help a worn synchro work better, at the cost of possible catastrophic failure in the trans. A bearing that fails will ruin every gear in the trans, reducing your once grinding transmission to brick status.