isn't the bottom chain tensioner (attached to the block, has a spring on one side of it and with a bit of imagination kind of looks like a golf club face.) the same in all 18r's thus you could steal one from a wreckers out of an 18rc (probably 2 bucks) and it is small and required on all 18r's(g or c or otherwise). so if you need it regardless and they are impressively easy to find at a wreckers and cheap, then this might be a suitable test case?