I am currently using synthetic oil in my 03 Jaguar. I have a slight oil leak but have not had it diagnosed to determine if the leak is coming from the seal or gasket. Would it affect my engine if I stop using synthetic oil and just use regular oil?
Type Oil on 2003 Jaguar S-Type
It may not but is always good to use the recommended oil by the Manufacturer i would use a stop leak if the leak is small sometimes it works pretty well.
I still have a 94 Saab 9000 which I always used synthetic. a couple of years ago it started leaking and Saab dealer used dye and cleaned engine-said I needed new head gasket. A Ford tech suggested I try mixing a couple of quarts of reg oil with the synthetic or use a blend. He said the flat platelike structure of syn oils which makes them great lubricants also makes it easy to leak out. I tried it and the leak stopped. Lots of people will ridicule this answer but I have the proof or lack thereof on my garage floor. try it and let me know if it works for you. I tried a stop leak before trying this - did nothing.
It wouldn't adversely affect your engine, unless you were no longer using the recommended grade of oil for your car. Changing the type of oil will not address the leak.