960 ignition switch not clicking

It's a UK RHD '95 960 2.5l estate The key sticks out of the column
at right angles, not out of the dashboard like the 740.

The ignition switch is even worse than my old 740. Rather than just
occasionally sticking, it has no detents at all and there's no spring to
return it from "start".

How awkward is this to strip and fix? Is it likely to be the switch or
the lock assembly ? Can I repair it and keep the old key, or do I need
a whole new assembly? Is a spare 740 switch block any use for fixing
it?

Thanks