It may be time for new seals again. Sometimes if there is excessive play in the guides, seals will stop the oil leak but it's only a temporary measure. As the valves move around due to the play, they stretch the seals and cause them to eventually fail again. 2 years sounds about right. If it were me, I would just do the seals again for about $30, and forget about the guides.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280