You don't mention how many miles are on your engine. If your engine is "seeping" any oil, it may become a leak when you switch to synthetic. Not that it definetly will, but it is known to happen. Also, synthetic oil likes like a cleaner in your engine. If your engine is gummed up in any way, synthetic wil loosen it up and possibly plug up the works inside. You could first switch to semi-synthetic, to "ease" the engine into full synthetic oil.
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
President of CT/Westchester Section