Mileage would be the determining factor for me. That and available funds. If they don't have huge mileage, leave well enough alone. There's nothing to suggest a brand new one would be any better anyway. If it ain't broke, don't fix it.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]