Daft question perhaps but have you tried lubricating the inside of the barrel? You could use WD40 but that is an oil and it smells. A teflon based lubricant is much better, or you could use GT85. Unless your barrel and key is very badly worn it usually works. Spray some into the barrel and keep working the key until it turns, but don't force it. You'll probably be surprised at the colour of the s*** that comes out.....

I've just done this job on our 1998 Voyager, straightforward with a good light a pozi 2 and plain small screwdriver. You have to be able to turn the key one last time to get the barrel out. Searching the ether consistently came up with the advice to tap the key to encourage the stuck wafers in the cylinder mechanism to fall into place, after a lot of tapping eventually the key turned. Once it is turning do not remove it as this will reset the wafers in the locked position. I left the key in position it will not lock again. I disconected the battery. I undid the plastic cowel around the lock by removing 3 pozi headed screws from underneath the plastic cover, separated the 2 halves of the cover which clip together at the sides, the top stayed place and removed the lower half. Look up towards the lock barrel, and I could see a small square metal button. While pressing this button gently in (up) I turned the key towards the run position slowly, when it gets to approximately the accessory position the button pressed in and the lock and key withdrew out. You could then take the whole lot to a locksmith who would then fix the lock and hopefully leave you with the same key as I think they are chipped. I decided to take it to bits myself. At the key end are 2 sping loaded plungers that locate the cylinder in the various switch positions. I pressed one of these down and could over rotate the cylinder so it was released from the barrel. Once out it was evident that it was the first 2 wafers that were sticking. Some careful cleaning and lubrication freed them up. I took care not to loose the spings and plungers and a very small lever that the tip of the key bears on that were released when the cylinder comes out of the barrel. If I'd lost these then it would be a trip to the breakers. I reassembled it all and it works. As it was the first 2 wafers that were sticking it may have been possible to free and lubricate then down the key hole with good vision and a good light but getting the barrel out was suprisingly easy.