So tonight I went about replacing the cracked exhaust header on the '81 240d and all went well until I looked inside the intake ports. They are caked with sludge and the valves are pretty disgusting.

Is there a "safe" way to clean out the intakes and valves without pulling the head? How about pouring in some MMO / varnish remover (with intake valve closed), let it sit for a bit and then suck it back out. But clearly this isn't guaranteed to keep crud from getting trapped in the valve seats.

Suggestions will be greatly appreciated as usual!