Daryl
I have a '66 230SL and have just gone through this exercise. As suggested earlier I used a spray bottle to pump out the old oil; it was quick, clean, and worked great. When I refilled the oil I used the same weight as in the engine, 10w40. 185-225ml of oil was not enough to fill to the max line on the dip-stick, as I recall I had to put in 250-260ml. I had an opportunity to talk with a Bosch mechanic about the IP, and how much oil to put in, he recommended just over a 1/2 pint, (@ 260ml).
The cap on my IP was also worn, I recently repainted it, used standard red paint; haven't had any heat related issues. And while I was at painting, I re-painted the engine's dip-stick red too.
Good Luck.
Scott
1966, Signal Red, 230SL