If this is a repeat post, forgive me, but I went through the same denial/acceptance process regarding some "easy" way to remove this asphalt-like crud from my 336 gbx. I am an aircraft mechanic by trade, and have access to many aggressive industrial-use-only cleaning chemicals, as well as a large Empire plastic media blasting cabinet. Nothing touched the worst of it.
What I ended up doing, and it was a nasty, labor intensive, filthy task, (and I'm used to nasty jobs, ask my long suffering wife / launderess) was to first use clay sculpting tools, such as these:
http://image.misterart.com/grouppix/528x352/000/g822.jpgto mechanically remove the gunk.
followed by a dremel tool with these, #428, #442, & #443 brushes. I bought these in bulk on ebay, and I bet I went through scores of them.
http://www.toolbarn.com/accessories/abrasives/wire-brushes-wheels.html?manufacturer=82I would dip the brushes in some of that gritty hand cleaner, and that helps alot, cleaning as well as preventing the crud from gumming up the brushes.
a full face plastic eye-shield is essential.
Like this:
http://tinyurl.com/9jpwlp2as well as some expendable clothing.
This is easily the most unpleasant Europa task in my four year journey.
If you are willing to strip the case of mechanicals & seals, cal44 has the answer; hot tank it.