My 98 V 70 has been doing this to a lesser or greater degree (ambient temperature dependent). It is caused by the mechanical portion (right side) of the ignition, and the fix is to get a replacement piece from the dealership. You have to call in with your VIN so that the replacement will be "keyed" to your current key. I'm getting mine for just over $100 US, so price is not bad. What takes a little is the fact that you have to drill the old one out, before you can reinstall the new piece. Here are a few sentences from Rich of Bay 13.
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I pull the steering wheel down and back. Remove the top cover, and the bottom (3 25torx) I take off the two stalks on the steering wheel, turn signal and washer, held in with you guessed it, 25torx screws. I push the connectors back into the dash best I can then I cover everything up with a rag to keep the metal from the drilling out of the electricial "Stuff". Drill, install, breakoff, clean up , reinstall electricial connectors etc.

Woops I forgot, there is a cable in the back of the ignition, put the key in position 1 ish, and you can work it out. The cable goes down to the shifter. Practice on the new part it will have a plastic clip in there like the one in the car.
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I'll be doing mine, probably this weekend, and if you want I'll let you know how it went. you can email me at hellcatdad@excite (add a .com) to the end.