Head gasket bad or just an oil leak?

i have a 95 ford explorer 6 cyl standard shift.. and it has an oil leak..i brought it to a garage and he said it was a head gasket but im not sure it is. I think hes lying to me to get the money, because im a woman. I have talked to many people and researched it online, and i just dont think that its the head gasket. It runs great, no white smoke coming out of the tailpipe nor any antifreeze or water dripping out, nor does it spit and sputter or have problems going up hills. It does not lose any power, its just an oil leak as far as i can see. Now..i havnt checked the oil yet to see if there is antifreeze mixed in or taken the antifreeze somewhere to test that either. A friend took it on a 6 hr trip,before we knew there was a leak and he said he had no problems with it. No overheating or hesitating or anything..he just had to put a little oil in it. It only leaks when its being ran, it stops after its parked.