A blown transmission is a blown transmission. A lot of 915 trans got screwed from poor maintenance including leaks that were not fixed and drained the oil, abuse from clueless drivers who "banged gears" and ruined synchros and gears plus just good old fashioned wearing out. The newest one is 33 years old now.
I absolutely love the 915 and would take one over a G50 car any day of the week. In fact, I don't like G50 911s and never have. I worked at the dealer when the new 1987 models arrived and I thought that they ruined the car...completely erased what was left of the character of the car w that generic weird transmission.
I realize that I am in the minority in the Porsche world but I also subsequently found out that while the G50 is a lot stronger, it's also quite a bit heavier and pushed the engine rearward slightly, (the last thing you want in a 911). The last 915s were fantastic w great shifters; any 915 was great if properly maintained but the last ones were the best. I also don't think that any aftermarket parts are needed in a street driven car but the condition of the linkage is crucial. Unlike normal front engine/RWD cars, the transmission is a transaxle and it's a long ways away from the shifter.
I also don't like short shifters and think that they particularly suck on 915s. They tend to remove the critical "feel" needed to artfully shift that transmission w/o "beating the synchros." Porsche did not win every endurance race ever created by having its drivers "bang gears" like a domestic rock-crusher at the drag strip. You have to know how to drive these cars but it's not all that difficult.
Driving a 911 really well at speed has always required a certain amount of skill and finesse. It's a huge part of the charm of the cars. The car is like a fine musical instrument and there is nothing worse than one that has been neglected or abused.
I had a rebuilt 915 w factory ltd. slip in my '82 911SC coupe and it was absolute butter. You could almost effortlessly upshift or downshift into any gear w proper rev-matching and steer the car w your right foot...it was heaven on a stick. The G50 was a stronger transmission and had to be introduced for the future of the model but the 915 was designed to handle up to about 300 HP, quite a bit more than any 911SC or Carrera of the time.
