I'm not a lawyer, and not familiar with US law generally, but I would suggest that if they accepted to do some warranty work for the initial problem it would imply that they were fulfilling their part of the contract with you - the fact that you are located in a different state could be construed by a layman that they are doing business there.
[did a law course long time ago - remember the bit about English law judging things in the "eye of a layman" - i.e. what an independent bystander would think of a given situation
]
But I digress, I think you should start writing letters, preferably to the top guy/girl - I know in the case of a large sophisticated (sorry I mean dead-end, Richard!) manufacturer with a name starting with D putting pen to paper to the head-honcho does have its effects...
Charles