oil leak?

Truck is a 1995, 2.7 liter that has 164,000 miles on it. I noticed it needed oil about 3 weeks ago. I put a 1/2 quart of synthetic blend that I had behind the seat from god knows when in it. The truck has never really burned or leaked oil before. I then started noticing oil in the driveway. It was due for an oil change so I had it changed thinking and hoping something was just loose, no luck. Since then I've driven 300 miles and had to put 1.5 quarts of oil in it. Tomorrow is my first day off and I plan on cleaning the engine the best I can and putting some dye in it. From the quick inspection I gave it it looks to be coming from the front lower passenger side of the motor. A friend said one possibility could be the oil pan gasket. How tough is it to change one of these out? Anyone have any other ideas of what it could be and how to fix it?

Thanks for any help!

 

I had a old Corolla that leaked oil like crazy, it turned out to be the oil pressure sending unit. It was cheap and easy to replace.