[svxistentialist]

The trade way of dealing with the gunge you mention is to use diesel.

When you have drained off most of the oil from the sump, put in a few litres of diesel into the oil filler.

Then start up the engine, run it for a bit and the diesel will dissolve the crud you mention. When you drain it this time, all the gunge comes out with the diesel.

Now don't keep it running till it seizes, and don't rev to the red line or anything. Diesel has inbuilt lubrication, but not enough to prevent damage if you overdo it.

A gentle wash. Like for delicates.

Joe