I'd be suspicious of the leaks at the exhaust nut, as they more likely represent thread problems, since--as previously noted--the sealing rings there are basically indestructable. I could only speculate that these rings might be damaged by having everything loose and consequently a hot jet of exhaust compromised them. Or, they could have been in salt water for a year or other such silliness.
Put (hi temp) antiseize on the threads on the heads and then get the nuts tight and check them frequently ... is the best approach.
A really nice set of photos of all the "gaskets" is here
Optimol TA is the best antiseize for this application--they don't sell stuff suitable for German vehicles down to Pep Boys.
#8, BTW, is the clamp--the gasket is #7.