Looking for some opinions regarding a an issue I'm having with a 65 C4 Transmission in my 289 Mustang fastback. The transmission was supposedly "gone through" a couple of years ago but it's always had an issue where when you start it and put it in any gear after it has been sitting a week or two there is usually a no engagement (no drive condition). The longer you let the car sit between startups the worse the problem. I'd put the trans is park and let the car run for a bit (5-10 minutes) and it would usually engage but would occasionally drop out of gear. After the initial 5-15 minutes of idle time in the driveway I would put it in gear, go for a drive and not have any issues. I thought it may be related to some sort of fluid drain back because the car usually sat a week or 2 between cruises but one time after the typical 5-10 warm up and a couple of mile drive, it dropped out of gear (shifter still on the green dot) when I stopped hard at a stop light. I gave it a little gas a couple of times and it went back into gear. No problems for the rest of the 30 mile cruise. Fluid level is good. Any ideas? I picked up a 66 C4 that I may try to rebuild myself but was wondering if there may be something simple i'm missing like a band or some other adjustment.