My first impression is to suggest that you find another machine shop. It's obvious there's something wrong with their procedures, or the clearances they're using on the valve guides. If a valve is fitted too close when the head is off the engine and cold, it will sieze up when it reaches running temperature. 3 tries is more than enough to establish that the shop either doesn't know, or doesn't care about doing the work right. If mecessary, box up that head and send it to me!
Jerry
