Oil Question Leaking

OK well I just purchased a 1992 Legacy Wagon AWD with 214K miles on it. I drove it about 400miles with no oil leak. THEN i get an oil change and bam oil leak from hell. I just would like to hear the thoughts of some of you.

This is what i think happen. With the change of oil it conditioned or lossened some of the dirt holding it in, then bam found a leak due to the cleaning deturgaents in the oils found in today's oil products, I used the Quaker State High Milage oil 5w30 with a fram 10K oil filter, BTW it is leaking around the oil pan, I did double check and the filter and drain plug are on tight.

Amsoil is on the way but dam not going to put it in the car if it leaks that bad LOL..

Thanks for any imput.