Both the M5 and M6 euro versions employ the same power plant - on my specification fische it's referred to as an m88/3. They took it right out of the M1 and slanted it into these cars with some mods for street use. The only coolant drain plug is on the engine block, under the exhaust manifold, near the 6 hole. I use a 1/2" drive ratchet with 19mm(i think) socket and do the job by feel, as the plug isn't visible from up top. I guess you could use a mirror to see it. Draining the block is messy - liquid runs everywhere- but you don't have to drain the engine to change the radiator or hoses. A good partial drain can be accomplished by syphoning from the overflow tank (a 1/4 inch tube can be guided right down the large hose exiting tank under side) and then from the radiator (again a flexible tube used to reach down the side compartment of radiator through the hot intake neck on upper passenger corner). hint : a US M radiator is at least a hundred dollars cheaper than the euro and it's a direct fit replacement.

ever read the standard safety disclaimers in some how-to publications?? 1. don't drink antifreeze, and 2. don't stop the fan with your face.

Pulling the intake plenum isn't all that tough or lengthy a job, if you don't take a bunch of wasted steps like i did the first time. After removing the air filter/air flowmeter unit, go right to the removal of the 10mm nuts (12 of them) that secure the six "throats" to the throttle plate housings. DON'T try to remove the six rubber boots 'til you get the whole plenum on the bench. I just had mine off to renew the fuel lines and i replaced the single boot (about $35) to the air meter, but I reused the six boots to the throttle mechanism.
Paul Hahn
'84 ///M635 csi with 107k smiles.