Hi all: I do not know if this is of any interest, but I just recently repaired my R.O.B. and wanted to at least post something on it in case someone was having the same problem.

Mine had the same problem a lot of people's ROBs had with it sticking when trying to turn to the left. I figured out that it is a problem with this small triangular plastic piece mounted on a metal strip attached to a piece of circuit board. That small triangular piece was no longer perfectly smooth on one side so that it would not come out of the slot when trying to rotate left. The 5 slots are on the circular piece in the base that are seen when the robot rotates to one of the 5 positions to pick up blocks for stack-up.

Anyway, a nice guy I know on ebay sent me some extra parts for free and I was able to replace this part and now it works 100%. I imagine that oen could also resand that triangular piece and get it smooth again but I tried that and ended up destroying the piece I had

Hope this is of interest to someone.