Regarding the door slide bushings, the nylon bushings were round with washers on each side. The later factory service bulletin slides were also nylon but were oval in shape making a longer contact area on the aluminum rail. Consequently, there will be longer areas of wear at the slide contact. The slides that I have on my Darrin are oval in shape but made of delrin. Delrin is self lubricating like the nylon but are more resistant to wear and is not hygroscopic. The doors stay tight on the slides, slide easily, and do not rattle as doors with metal rollers do. The problem with the rollers that some folks were using, is that over time the rollers wear the aluminum rail. Also the rollers need clearance in the rail to roll and when driving the car the doors will rattle over bumps. I got my slides from Ron Meditz years ago. I don't know if he still has them or not. When replacing the slides, make sure the aluminum rails are not worn where the slides rest. I had to tig weld my door slides to get rid of the grooves.