I got my '76 450SL engine to run and now I need help on my '77 450SL (doesn't everyone have 2 SL's?). This is a good one BUT the 2-3 upshift will not occur until the system is thoroughly warmed up. I know my SubaruXT had a "thermal switch" in the transmission to lock out 3-4 upshift when cold. Once warm the '77 works fine. If the transmission must come out will a newer 4-speed auto work or is it sacrilege to consider this?