90% of all valve train failures are from lack of enough spring tension or proper interference fit from inner to outer. Practically every higher performance cam for a VW requires dual springs (inner and outer with proper interference). Only the very mildest of cams can get by with single HD springs. Even the stock VW cam must have HD springs if you turn more or quicker RPM through a lightened flywheel, head, or carburetion improvements. Your lifters must follow (track) the cam profile up and down. When this happens, the lifter never slams down or is slapped open because it only has the hot running clearance of about 0.010" to 0.012". If the cam follower leaves the cam, bounce or float may give as much as 0.150" of slam down.
This causes the same or worse damage to the rest of the valve train causing retainers to pull through, guides and valve seats to come loose, bends pushrods and will even cause burned valves, etc. This is because they are not gently picked up and set down on the seat (and do not bounce) like they do when they have proper springs and tension. For more information on cams and springs read GB 801-CAM and GB 801-SPRINGS.