You've thrown me off a bit when you mention "bobbin" in the context of a PGP 8.1. The PGP 8.1 is a layer wound coil. The difference is that on a layer wound coil you can see "into" the sides of the coil--- and hence the varnish penetration is really good inside the coil.
Your the first case I've ever heard of in saying that the coil appears to be loose on the lamination stack--- though it is possible. The test to me would be is the unit noisy when you use it? Remember both the coil and the lamination stack have both been impregnated (i.e., varnished). The likelihood of either of them being noisy is not very likely.
Try them out and get back to me. You can reach me at acrosound at aol dot com. Out of curiosity are you the original purchaser or did you get these from someone else? The reason I ask is that we have not sold these for quite some time now.
Mike
Builder of MagneQuest™ & Peerless™ transformers since 1989
