Worst case, manual trannys are easy to rebuild ...and generally not very expensive if it's just worn synchros, synchro collars and shift bushings. If you have one that needs some work, something to consider. Then yer good to go for a long time.
Also know that different lubes can affect how they shift. Shifting works by engineering a known amount of friction into the synchros. And as synchro rings wear, the friction surface area changes (generally increases slightly). Switching to an oil other than what is factory specified may be "slippery-er" or less so, and throw off the shifting. I've experimented with different oils and lubes on some manual transmissions I've had (Toyota's) that I personally rebuilt both. I used to have two exact similar trucks with the same setup. Yeah, you could definitely tell the difference between different lubes in shifting. Going with a so-called high-end synthetic gear lube, for example, might seem like a good idea, but it *could* affect shifting negatively. Maybe yes, maybe no. It'll probably have some slight different characteristic even if minor. So my recommendation is to buy the right GM stuff, when you get your tranny installed at least to establish a baseline before trying something else.
