Thanks for the replies all. The Chinese made adapters I bought look like the one below. I assumed they were pretty much exact copies of the Pentax branded ones.
It appears the cheap knockoffs are the issue. From the responses above, it appears if I buy this design in the proper Pentax adapter, my M42 lenses should mount dead straight up. Expensive, but that's life.
Anyone know the cheapest place to pick up this Pentax adapters these days?
Also, given how cheap they are, I might give another Ebay vendor a go. If anyone out there has had better luck with the knockoffs, please let me know which vendor you purchased them from.
Cheers!