I don't think there's an easy answer to this one, but here goes anyway just in case anyone has any suggestions...
Red '98 Spider, while reinstalling centre console and wanting to test the lights, I pressed the button under the ignition key, and turned the key backwards to 'Park'. Side lights and heater control lights etc. came on, great.
Then I found the key would turn forward (to 'Stop'), lights went off, but the key won't turn any further!
Thinking the steering lock was engaged, I refitted the steering wheel (which happened to be off) and turned it. Then the steering lock really was engaged, and the key still wouldn't turn clockwise past Stop.
I tried fastening the steering wheel on properly (doing up the nut), in case the column has slipped inwards, but no change. I used the spare, unworn key for the car. That turns more easily to Park (with button pressed), and back to Stop, and it's easier to pull out and put in. But it won't turn past Stop.
I sprayed in lots of penetrating oil, which again made the key easier to turn between Stop and Park. I have tried turning the steering hard against the steering lock in both directions while wiggling and turning the key. Still the key won't turn past Stop.
I even tried the key from my other Spider. That won't turn to Park. It's easy with the right key, therefore, I think the lock tumblers must be working.
I feel that the steering lock has somehow jammed, even though the steering lock wasn't even on when the key first refused to turn.
Of course now I can't get the steering wheel off, so I can't get the column covers off - two of the screws are obscured by the steering wheel, which obviously can't turn. In the morning I will use an old pair of small pliers, some washers to span the handles, and a couple of long bolts in the specially-threaded holes, to draw the wheel off the column.
After that I guess I will remove the lock barrel and if that's no help, I'll have to drill/grind the steering lock off the column...