<VV> Oil Pan Leak Question

[Bill H.]

                                                                                            B"H
Hi folks, hope everyone had a Vairy nice summer :-)
I'm having a problem with an oil pan leak which is driving me nuts.  Oil was leaking from the bolts, drip, drip, drip until (I am guessing) the oil level goes below the top of the pan.
I have an Otto aluminum oil pan, which is rigid and in excellent condition.  I replaced the gasket with a new rubber one from Clark's, tightened the bolts according to specs (100 inch pounds) but the leak persisted.  Every time I checked the bolts they seemed loose, so yesterday,  I installed lock washers on each bolt.  Now, oil seems to drip only from the bolt farthest from the rear of the car, no matter how tight I made that bolt.  The other bolts seem to have stopped leaking, but you can see the dripping when you look under the rear of the car.  
By the way, when I installed the gasket, I made sure it was flat and I used a thin layer of grease to hold it in place when I installed the pan.
I don't drive the car much, maybe once every week or two.  When I checked the oil today, it was between the FULL and ADD marks, and there isn't any noticeable oil loss when driving the car, just when it's parked.
Can anyone help?  My car's a 1966 Monza 4 door hardtop, 110 engine, PG.
Thanks all!
Bill Hershkowitz