Hot Rod magazine published an article in the June 2006 issue on the topic of flat tappet and cam failure caused by changes in the formulation of motor oil. Tappet is another name for lifter, as also is follower. Although it is written with the big displacement Chevy/Ford/Mopar engine crowd in mind, this article is still of use to the aircooled VW crowd since our cars come with flat tappets.
The article is found at:
The solution to the problem is to use oil that still has the ZDDP additives. The article mentions (with accompanying image and caption) Shell Rotella as one of those oils. I found Rotella at Pep Boys for just under $9 per gallon, which makes it competitive in price with the non-ZDDP oils. Racing oils usually have those additives too, although they don't usually make a point of it in their advertisements.
Gene Berg came out with a discussion on this same topic in their newsletter dated April 1998. His shop, and others in the business, were having trouble with cams going flat. Berg bought an additive containing moly, phosphorus, and zinc to add to the oil, and the cams stopped failing. I tried to find mention of this in the Tech Tips section of their web site but came up empty.