I personally haven't had any problems switching to a synthetic oil on a used vehicle.

At about 50k miles, I began using synthetic oil in my VW Jetta TDI. It now is pushing 200k and still doesn't leak or use oil. Also switched oils in my Cadillac V8 at around 90k. It now has 110k with no adverse effects. The MB started using synthetic in 1994 and 100k later, has not experienced any problems oil-related.

One word of advice though, if you plan on running extended intervals, it wouldn't be a bad idea to use a diesel-rated synthetic. Not so much an issue if you change at 3-5k miles, but if you are going to use a 10k mile interval, the diesel synthetic will handle the soot load better. I've done oil analysis both ways and there really a clear difference.

Keep us up to date!

__________________
Lance Allison
Lance@LanceAllison.com

Current:
11 MB S550 4Matic, 55k miles, Designo Black/Black
14 Ford F150 XLT Lariat Crew, 73k miles, 5.0
Coyote V8 4x4. Black/tan.
09 GMC Envoy Denali, 5.3 V8, 4x4 SWB. 38k miles,
Jewel Red/Med Gray.

Gone:
87 MB 300SDL, 320k miles, Astral Silver/Blue.
98 VW Jetta TDI, 488k miles, Classic Green/Gray.
85 Olds 98 Brougham FWD, 4.3 DIESEL V6, 80k
miles, 3x Gray.

MBCA Member, Chicago Region