We have a late 1960's air cooled flat 6 race engine (8400 RPMs; 2.0 litres 245 HP) that has started to consume camshafts and followers since we changed* from SL oils. [*]ran out of our stock of SL oils on the shelf. We used to get 100+ hours on a camshaft (3-4 rebuild cycles) and almost never wore out followers. Now a single 3 hour race and the cam has a nice 0.100" deap grove worn in the middle of the lobe where the followers touch and the followers are toast. We had the worn parts checked for hardness and they measured in at spec. This situation occured on a run with M1 15W-50 and with RedLine 15W-50 whereas it did not happen last year under SL oils. I suspect that a lack of ZDDP is involved. Where can I find an addtive that is almost completely ZDDP? Or: Can someone suggest other lubrication issues that might have lead to this situation?