thermostat housing leak again !

[jpliddy]

hi all
its been a while now but my thermostat housing has decided to leak again the leak is small as its just got staining down the engine block,
did the d24s ever have a gasket the flat mating surface ? , last time it leaked a while ago i used hylomar blue its lasted probably a couple of years nearly i think i just don't like to see any staining on the engine block ,
i have seen a gasket supposedly for volvo d24s and petrol engines too on ebay !
do you have any suggestions on this subject , regards jim