Hey Dirt71,
Check your rear idler axles / pivots for excessive wear. Ours where worn to the point that it allowed the rear idlers to "toe" in. The outer halves of our rear idler sprockets were almost worn through buy the track center guides. I was able to find replacements for everything since ours were junk. Normally there is two grease zerks per pivot, I installed four on each one to improve greasing since the pivot does not fully rotate. The volute spring perch / crab assembly are usually rusted solid. After replacing ours I installed a grease zerk between the volute springs to allow greasing of the center pin. I even added grease zerks to each of the 8 bogie support arms. These require drilling two holes at 90 degrees of each other since the bearing point is at the top of the arm. It was fun since they are hardened steel. These vehicles have already survived 70 years, hopefully these efforts will prolong the life of these irreplaceable parts.
Your M3 looks great, thank you for saving a piece of American history.
Karl