'72 915...rebuild or replace? Help!

[Roger 911]

I have a '72 911 with a 915 that has been a thorn in my side for two years. I have had a recurring problem where it will bind up preventing access to the 5-R plane. I took the tranny out this past summer and discovered that the rod for 5-R had somehow rotated slighly preventing the dongle from moving into the recess for that rod, which then allows you to select either 5 or R. I simply applied a bit of pressure to the rod and rotated in back into place, aligning the detentes on the rod with the detentes on the 1-2 and 3-4 rods. This worked great at first. Everything was back to normal and I was able to shift wonderfully, until I got to Road America, where the same problem reoccurred. This leads me to believe that something may be bent inside.

Fast forward. I'm in the process of removing the engine and tranny from the car and I manage to snap off the threaded male connector for the speedo from the front tranny cover. This now has given me reason to ponder my long term relationship with my early 915.

Points to Ponder
1. I know '72 is essentially the worst year for the 915, with the goofy main seal design.
2. I plan to Club Race and or Vintage Race the car starting next year. I'm concerned that the mag case may be more trouble prone in this environment. I know these cases can be modified substantially, but I'm not looking to spend $5-10K on my tranny right now.
3. If I change to a later aluminum 915, will the 8:31 R&P be a real "downer" for my 2.4 engine?

I realize that it will cost me about as much to get a used later model 915, including the new axles and speedo, as it would to rebuild my old 915. I'm a bit torn. I know on one hand you can say it's better to rebuild what you have then you know exactly what you have. However, I'm concerned that a '72 915 may not be worth it (some builders won't even rebuild them, e.g., Gary Fairbanks).

Thoughts?