We normally change them all once one starts to tick...There is a chance that you exchange the wrong one or that one of the other hydraulic lifters will start ticking once you (think you) are finished...

The price of a hydraulic lifter is reasonable enough to exchange them all at the same time...

greetingz,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)