Need your help to solve this mystery:-\

 

Vehicle: 2001 Forester S with 104k miles

Diagnosis from Smart Service, Seattle, WA during buyer's inspection: medium oil leak from Left Head Gasket (HG) & minor leak from Right HG (even though seller had replaced full HG Set <1 yr ago). By "medium" leak, the mechanic explained that if the car was left idling in one spot for a few minutes, there would be drips from the Left HG.

Seller: Injected florescent dye into both coolant and engine oil over this weekend and drove over 200 miles. When he took it back to his HG mechanic today (still within 1 yr warranty period), there was absolutely no leak (no florescence).

 

Assuming that neither mechanics are wrong, is there a rational reason why there would there be a significant leak found last Friday but no leak found after driving 200 miles this weekend? How do I resolve this mystery quickly and decide whether or not to buy the car? I trust both the seller and the mechanic. At this point, the seller is really pissed off at the inspecting mechanic and just want me to decide to buy the car or not by tomorrow AM. Your expertise appreciated!

Need your help to solve this mystery:-\

 

Vehicle: 2001 Forester S with 104k miles

Diagnosis from Smart Service, Seattle, WA during buyer's inspection: medium oil leak from Left Head Gasket (HG) & minor leak from Right HG (even though seller had replaced full HG Set <1 yr ago). By "medium" leak, the mechanic explained that if the car was left idling in one spot for a few minutes, there would be drips from the Left HG.

Seller: Injected florescent dye into both coolant and engine oil over this weekend and drove over 200 miles. When he took it back to his HG mechanic today (still within 1 yr warranty period), there was absolutely no leak (no florescence).

 

Assuming that neither mechanics are wrong, is there a rational reason why there would there be a significant leak found last Friday but no leak found after driving 200 miles this weekend? How do I resolve this mystery quickly and decide whether or not to buy the car? I trust both the seller and the mechanic. At this point, the seller is really pissed off at the inspecting mechanic and just want me to decide to buy the car or not by tomorrow AM. Your expertise appreciated!

Are we sure it is a HG leaking oil? That vintage leaked coolant externally as I remember and the replacement HG would have been covered up to 100K/8 years. Is it possible that the valve cover grommets around the spark plugs are the culprit? This is a common problem with that year.

If it is a HG leak, is it possible that someone put some "stop-leak" in oil?

Is the warranty transferable?

How much of a headache can you tolerate?

Ask the inspecting mechanic to demonstrate where the leak was... was the engine cleaned since his inspection?