Need some transmission advice

[Mr 5 0]

Will your C4 make it a few more months? From what you said, it doesn't sound like it. That's your immediate consideration. Not much fun to put it in 'drive' hit the gas and sit there revving while the car creeps forward.

On that basis, I would certainly have the C4 rebuilt which will give you plenty of time to continue to save up for the Lentech and still have a transmission you can sell for a reasonable price later, instead of using it as a boat anchor.