The 3 things we have found to cause that .... 1. not changing oil regularly ( at least every 5000 miles, 2. Not using 5w-30 oil and 3. not reving engine enough , yea believe it or not , not running the engine to 6000+ will cause the oil pressure to not get to its peak and that will cause the oil tubes to clog and then cause cam wear, same as using an oil thats to thick, that will cause the oil to clog up the tubes, but I can say I have seen a few that have run heavy oil, but rum hard that never have a problem .... We rarely see this problem on Hot Rodded Sr's , usualy on G20 Autos that are not taken care of and not reved enough, reapair requires new cams , rockers and oil tubes !!