c280 water pump r&r
I noticed nobody answered your question of what it would take to replace the wp. I just did this job on a 1991 300TE with the M103 engine. I believe the C280 has the same engine with a smaller bore, same block and everything. Book rate on an M103 wp is 4 hours, if I recall (Larry Bible help me out if you can). I did the serp belt tensioner, shock, water pump, and air pump all together so I can't give you an itemized list, but I'd guess over 4 hours for a DIY after you get the fan and shroud off, etc...
Very do-able if you have the ambition, I hate to pay others for work I can do as well (IMHO).
YMMV. Good luck!