sink drain problem

I have a old model Crane pedestal sink which I disconnected to facilitate new wainscoting. I replaced the p trap with a new one. After reconnecting everything and turning on the water I have leak coming from the drain where it exits the bottom of the bowl at the washer. Most likely from all the jostleling getting it reconnected. I removed the p trap and tried tightening the drain but the whole thing spins in the hole and I can't loosen it for removal either. This part looks to be original. I would greatly appreciate any suggestions.
Thanks, Brian

Loose but can't remove.

That is a tough one.

Do you remove the old drain and use a new one?
If you do, you can saw or chisel off the old parts.

Do you keep what you have?
Sometimes you can loosen the nut below the bowl and drop it enough to put some sealant in there.

sink drain resolved, one more question

Thanks for the reply. I sprayed some wd40 onto the threads in the drain and stuck a piece of rod into the drain to keep it from turning and it I was able to remove the nut. No damage done, I'll be able to reuse the parts. One more question, what should I bed the drain in where it seats on the porcelain. I plan to replace the washer but it seams like some type of pookey is needed on the inside part as well.
Thanks, Brian