I have a vintage sink that I have removed all the fittings in order to rebuild them. The spout is being difficult. The inlet is threaded into it and due to the 70 + year old pipe compound and/or plumber's putty it is stuck. The underside of the sink is recessed, the retaining nut has been loosened, but I can not get leverage,( tried basin wrench, nicked threads), used a little heat, no luck. Is there something I can apply to the joint to help loosen or dissolve the adhesion? The sink is not mounted and there is now enough space to apply something to it. Tried WD-40. Thanks

I have a vintage sink that I have removed all the fittings in order to rebuild them. The spout is being difficult. The inlet is threaded into it and due to the 70 + year old pipe compound and/or plumber's putty it is stuck. The underside of the sink is recessed, the retaining nut has been loosened, but I can not get leverage,( tried basin wrench, nicked threads), used a little heat, no luck. Is there something I can apply to the joint to help loosen or dissolve the adhesion? The sink is not mounted and there is now enough space to apply something to it. Tried WD-40. Thanks
You only have two options here. 1) Soak it in WD-40 and try with the basin wrench **or** 2) Split the nut with a Saws-Al and peel it out. There may be a third if you can get your Saws-All blade between the nut and the sink you can cut the threaded inlet out.
Good luck, Tom