I stick to MB brand coolant or Zerex G05 for MBs. No idea what coolant is good for Volvos. Can't imagine G05 is bad for any car.

I believe your S420's 5-speed AT requires MB's special ATF for the 722.6 transmission. Not a big deal since you probably don't have the means to check or fill the transmission. Again, no idea what ATF works for Volvos.

Sixto
95 S420
87 300SDL