oldfart, that is a good tip for anyone looking at used '78 model RM swingarms in all capacities (excl. 80,60,50) they are indeed thin and do flog out at the slightest hint of bearing/bush wear
when I was 16 I binned my then near new RM400 arm for this very reason..obviously in hindsight I was very silly yet again
I purchased a brand new item over the counter at near $180 from memory and then 5 years later it too became unusable. I tried to have it repaired by a local aluminium welding shop but that was a bigger mistake as they wrecked it even more
I then switched to a '77 RM370 box section steel job and never had another problem for untold years
Only in the past 2 years have I found another 'affordable' 250c2 swingarm and refitted that but I'm keeping the steel item up my sleeve as a failsafe. PE250B also have basically the same arm as the 370 though not sure about shock positions. Bit of dribble but it does relate to the DRM as most go for the alloy '78 RM arms when there is little advantage excepting appearance. Problem with the PE arms is it's hard to find one not overly rusted out underneath at the rear. Depending on the rust severity this for my mind can be fixed easier than the alloy RM arm which will continue to need constant inspection. If someone offers up a 370 or PE250B item at the right price then it's a good asset to have up your sleeve when all else fails
