Well, if I understand correctly, I give some options here,

The first one, is can you pin it to the shaft wil the pin going all the through.

Pin has to be large enough to handle the shear, down side of this is that it may take away the strength from the hollow shaft.

phoenix911

taper lock bushings will clamp a round the shaft.

may not be a problem seizing, but in a soap environment would it hold?

Clamping force put on the shaft by a taper lock should hold even with the soap. Even under extreme load as if the scrappers bound up if it did slip so what. Your pin may have sheared off or the scrapper blades broken. Pretty hard to say sight unseen. picture are nice help but not like being there. He was looking for options.

What I question more is he said the drive is hollow whether it would deform it.

Personally if I had 6 others that where the same and only the one has the problem than some thing is wrong with it. All the options we give him may fail due to the cause of problem. May just be an alignment issue blade scrapping too hard against the surface.

Yes like a bend shaft

thanks for your valuable suggestion. let me try this good idea.

First of all

Force required to scrap > Force holding the joint assembly with hollow shaft.

Hence:

1.Sharpen the stirrer blades and

2.Provide Bolted Flange joint with teflon Bushes in between (like coupling) or else go for universal Joint in extreme case.

This will solve your problem.