do check on your oil level or lubrication system first before proceeding to replace the hydraulic lifters, as they hardly failed unless your have a very very bad sludge issue.
start with checking the oul level. if oil level is correct, check if you are using the right weight oil, if its correct, proceed to check the oil pressure. loose oil pump nut? failling oil pump seal???
why do i recommend the above?
well i had a similar problem on my previous ride. spent tonsss of money to replaced the lifters and still the same problem. so i just crank up the radio and forget about it. then a few mouths later, my oil pressure ligt begin to blink while idle in D. oil level was ok. check this and that and finally found the cause to be a loose oil pump nut, which is a common occurance in m50 m52 and m54s as well. had it thighten and spot welded it. to my supprise the ticking sound disappear, it was totally silent. after much reading, i got to know the oil lifters function with oil pressure, if the oil level is low, or in my case the oil pump is weak, the lifter will not be getting the right amount of oil and thurs not extend to the proper adjusting length. using a low viscosity oil will also cause your lifter to tick as the oil is too thin to be retain in the lifter body, thats the reason when some bmwgurus will ask you to use a thicker oil to cure the ticking problem.
on a more recent encounter, my current ride made some ticking noise suddenly just the a few weeks back, and upon checking i found my oil to be way below the lowest mark, no thanks to a oil sump gasket. fixed the leak and top up the oil and its running smooth as it should be.
