Before thinking lifters, look to the crossover supply pipes in the area of the noise. the plastic pipes that started about 94 have a closing plug that falls out leaking the supply to that set of lifters.
There is a service bulletin about it and even pictures here in the archives. Very common problem. AND considerably cheaper both parts and labor.
I would just replace the one that failed as there really is no risk as long as you don't drive it for years that way. The last one I did had probably been bad for a year as the customer had been scared badly by similar expensive illusions. If another fails it will just make noise in the short term.
The replacements are built similarly although they may be using better glue.
Bosch Master, ASE Master, L1
33 years MB technician