Hope it's not serious....
Driver side oil, eh? Well, you've already mentioned oil filter, so let's see, it could be the oil pressure sending unit, right above the oil filter, and another one next to the distributor(and a pita to get to), and, if your '85 has the HD cooling system, you'll also have the engine oil cooler, and the adapter for same that the oil filter screws onto.
Those are the main oil leakers, so unless you have a big hole in the side of the block, your leak is prolly coming from one of those items. All are fairly easy fixes, except the oil pressure sender next to the distributor....that one will have you saying words you never thought you would say....
Could also just be a valve cover leaking, but those usually don't leak that much...unless you forget, and leave one off altogether...
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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"