I would say it all depends on how your initial conversation went.  If you called them and told them about it, and their response was that they would try and get parts for it, and then you offered to get the used parts instead, I would think that the travel is up to you.  I'm guessing that a head that old wasn't much money to start with and if this process gets too expensive, they're going to balk.  I'm not saying it's right, but from their perspective, there's probably not much money in this deal as it is.  I guess it wouldn't hurt anything to mention it to them and see what the response is, the worst that can happen is you end up eating the extra cost, since you need to fix it anyway.

Mike