[Mad Mac]

Just to clarify, the blockage is not some kind of "gunk" that can be easily removed, it is the old horn tube that has rusted solid inside the shaft. Drilling it out with a drill-bit welded to a long rod was getting small, one-inch-long bits of the horn tube out, but at great risk of getting the drill-rod stuck. And if the rod gets stuck that will definitely be the end of it. BTW the horn tube cannot have been made of aluminium because there is a lot of rust inside it and the few pieces I got out appear to be some kind of thin-walled steel tube.

I think a better option is for me to use another steering shaft I have, which has no obstruction inside. However that shaft has quite bad scoring above the worm. I have heard conflicting opinions as to how important such scoring is and how to remedy it. I would value opinions on that from you helpful guys.