Diesel tank lid seals

[tugboat]

I've just started opening my keel diesel tanks to empty, clean and debug. Steel boat, steel keel, steel tanklids. Having anticipated finding nitrile joints under the lids, I'm instead faced with a load of sealing compound of some sort which is making the lids a right bu**er to prise off. The sealant is set into a soft rubbery consistency and is the colour of red Hermetite. Anyone know what it might be? It's proving incredibly difficult to clean it all off in order to use a gasket next time so may have to resort to using the same stuff again, if someone can identify it. Thanks for any suggestions.

 

[VicS]

If it is red Hermetite meths should clean it off

 

[tugboat]

It isn't Hermetite, I just used that reference to describe the colour. It is a sealant that has been applied by mastic gun. It is not as hard as cured Sikaflex, more a soft rubbery finish like silicon mastics. It is obviously diesel-proof, but I have never seen a sealant that colour and was hoping some forumite could identify it from the description.
Surely the gang aren't stumped? /forums/images/graemlins/shocked.gif