I agree with the multiple suggestions about soaking, and judicious use of heatAny suggestions of how i can remove this without damaging my regs? I dont mind damaging the adapter.
I agree with this approach, if it is possible.edward3c:Can you not remove the DIN from the 1st stage then you only need to soak etc the two parts you want to separate.
If it was my gear, I would, in order: a) put the regulator / D-T-Y adaptor unit on a yoke tank, take a set of channel lock pliers, and try to turn (loosen) the handwheel. I know, several posters have said nix the pipewrench, but this would be my first approach. I have used this technique before, several times, without damage to the plastic handwheel (other than minor, cosmetic, scratches), the D-T-Y adaptor, or the DIN bolt on the reg, etc. - obviously, use good judgement about the application of force. I have also successfully used a small pipewrench, on the handwheel, and tapped it with a rubber mallet to break the seal caused by the corrosion; then b) remove (if possible) the DIN bolt, with adaptor attached and soak it in warm solution - personally, I prefer to use the GMC cleaner - it is the best solution for cleaning I have ever used. You could also try the variously suggested solutions of vinegar, Simple Green, or even water. The key is warmth and liquid; then c) take the unit to a local shop and pay them to remove it.
You mention that you don't worry about damaging the adaptor. FWIW, the DIN bolt itself (on the regulator) is probably less expensive than the adaptor, and is easily replaceable.
Good luck.