Not familiar with the E4 but on the one piece six sump the gauze piece can be unscrewed and sloshing with petrol or other solvent, draining and repeating. With the gauze removed you can get a bent wire or similar down to dislodge caked sludge. Continue till nice and clean.
Others may have experience with other methods such as pressure cleaning methods.
Good luck.

The splash tray has small holes in three of the troughs. Is there a best way to repair these?

Would think soldering would do the trick but have not had that problem to deal with.