All right, I'll bite. After spending 9 hours to R&R the head and another 5-6 to do the machine work, why would you even consider not replacing some guides? If they are all within spec its one thing. If any are out the others have been on the same trip.
So you have one or two out of tolerance after 100-200k, how long would you like your work to last. Guides are like 8 bucks a piece. I never go cheap on materials.
Bosch Master, ASE Master, L1
33 years MB technician