My 305 is driping oil from the bottom of the oil pan..it loses about a quart a week just sitting there with or without being run. I can't seem to tell just where it is coming from, there is a wet spot down the side of the pan, but it looks dry above that. Could it be the pan itself or is it more likely the rear main? Any advise would be great.

 

Clean up the pan and find out where the leak is.

It could be the pan gasket, could be the rear main seal, could be the front main seal, could be the drain plug, could be the filter gasket, could be a valve cover gasket...etc.

 

Last two oil leaks mine had were from the oil pressure switch, right above the oil filter on the block. These damn things tend to start leaking right between where the metal and plastic meet.
Cost about $50 too! Last one only lasted six months!
Good thing I kept the receipt.
Anyway,you might wanna check it out.
-Rich-

 

As was mentioned clean up the area and see where it's coming from.
I just changed mine. My pan rusted through and was leaking directly above one of my exhaust pipes.

 

50 dollars for an oil pressure switch?? Are you kidding?? I guess it's a gauge-type, not a light-type? I replaced mine a week ago and got the switch for something like $10. I can't find the damn receipt. Maybe you should double check that price at some websites...

 

Yep, gauge-type switch/sensor.
-Rich-