I need to replace the heater levers in my 108, as all are broken. While I am in there I am debating whether or not to pull the heater valves and replace the seals. I plan to follow the guide outlined here:

http://w108.org/articles/heaterlever1.pdf

My question is, and I know it is addressed in the guide. is that if I pull these valves, how much coolant can I expect to leak out? Should I drain the coolant system before doing this, just place a pan in there or rag?

Thanks