Finch? the warranty does not forgive us nothing but considering it has to do at his own expense the change of a monoblock ? a drain..
you want that after 90k miles, the engine is open does not make at least the bands and bushings new ? head gasket, studs and more.. 2000 eur ? the minimum..
maybe if c'? a passage blocked you try with additives + aggressive.
At the end of the fair, however, to blame ? the engine oil, I gather..