If you can feel it, it is in failure. You can get some more life with a new rocker arm. If the original shape is intact it may go a while. If there is a dip where the loading is greatest it won't last long.

I looked at the cam numbers and I see no motors but 3.5 motors using the 52 and 53 cams. What is your chassis number.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician