I'm thinking of switching to synthetic on my 740t with 150k mi. 2 questions

1. Will this enhance the small leak I have now and is it much to fix?

2. Do I continue to use the same viscocity? I currently use 20W-50 living in Florida. By the way replaced turbo at 130k mi.

Synthetic oil is great stuff, and I've been using it in my cars for almost 25 years now. However, it is not a cure-all or a mechanic in a can.

Synthetic oils will not attack gaskets or seals. In some cases, synthetic may soften them and thus stop some minor leaks.

If you have a leak now, figure out where it is as step one. If the oil pressure sender unit or valve cover gasket are leaking, thats a pretty easy fix.

I use AMSOIL 0W-30 in everything--- 85 Saab 900T, 88 Saab 9000T, 85 Volvo 245T, 1 ton Dodge van. Unless you have a worn engine, there is no benefit to be gained from using a higher viscosity synthetic. an xW-30 should give you plenty of protection.

Since you have a turbo then syn oil is the way to go. As for your oil leak, where is it? Some say syn oil will leak more while others say syn oil may make the seals swell a little stopping the leak.......personnaly, I don't know (this one's for those Amsoil guys)

You should probably go for 15-40 syn oil since this is the best balance between light and heavy oil.