[Fasterthanyou]

I'm not off kelter on this one BUT, most aftermarket heads don't see the miles as a set of OEM heads. For this reason, and the fact that OEM almost always has the better toleranced equipment, the heads last longer. This is just an educated reasoning for your bad luck. It's not the first time I've heard of AFR heads needing the guide's done. Where as OEM expects to meet emissions standards on thier vehicles for over 100,000 miles mechanically... the aftermarket could care less. Dart, TrickFlow, AFR, Edelbrock, Canfield, all of these are out to make a profit so their tooling might not be top notch on a production run. Quality control is there but it's not a fraction of that from the OEM.
All in all don't feel like you've been gipped. Those heads are great but with anything there are compromises.
The one thing that's misleading is that you're burning oil THROUGH the valve seals. If they're teflon this is possible but with the normal ubrella street seals it takes a BIG valve guide problem to start burning noticable oil.
The last thing I can think of is your oil ring was installed wrong. It's common for the oil retention ring to overlap itself causing it to be pulled away from the cylinder wall. This will kill a cylinder eventually and show up as burning oil while the compressiong rings are still good.
Also, I can't remember, did you install new spark plugs? Sometimes just a bad spark plug can cause wash down. New plugs, try it out.