Rear main seal

I have a 94 sentra that leaks oil badly. I have had it in the shop and replaced the oil pan gasket and several others already but that didn't fix the issue. They want about $450 to fix the rear main when they unnecicarily replaced the oil pan gasket in the first place. Is that price too high?

Is it even worth it to give this product a shot?
http://www.barsproducts.com/product.cfm?id=50

I don't know a great ammount about automobiles, but when I see formulas like that I generally back away from them... far away.

It is snake oil at best.

If a shop incorrectly diagnosed your problem, and now wants to replace the rear main, I would be looking to have the cost of the oil pan gasket work taken off the price of the rear main work. Any reputable shop first off, should have correctly diagnosed the issue, and second, if they did mess up, they should be willing to go half way on the deal. If they wont budge on the price, I would ditch that shop, and go somewhere else.

Yeah they gave me 10% off which is nothing for a $500 repair. I am going to shop around when I get a chance. The shop is claiming that I had 3 major leaks that all started at the same time. Oh and my PCV system is working fine so it didn't blow out the seals.