The valve guide oil seal problem is so pervasive and so easy to solve that it ought to be included at 100k servicing IMHO. The 2 to 2.5 hours it takes combines readily with spark plug removal and valve cover resealing (leaving only an hour or hour and a half extra labor) which would already be part of a large service done around that time (maybe the 120K service).
The rings are never the problem!
Bosch Master, ASE Master, L1
33 years MB technician