[elgyqc]

My problem was that on both my Boxsters the key would go in fine but turning it was difficult to the point of being afraid to break it. I read up on the possible solutions and crawled under the dash and with great difficulty removed the electric switch. Tried the key and the problem was still there, so the binding was in the tumbler section.
Other threads suggested the problem comes from contamination in the tumbler mechanism (dirt, hardened lubricant and metal that has worn off the key etc.). With this in mind I squirted contact cleaner in the key slot then blew it out with compressed air, followed by graphite powder as a lubricant. This worked, I had to turn the key a few times to get the graphite spread arround but the key became easy to turn and I finally heard the clunk that I read about that you are supposed to hear when the key is removed.
This worked for a week or so and then the difficulty in turning the key returned and it no longer clunked on key removal. I repeated the treatment and again the problem was resolved. The car is put away for the winter so real life testing will continue next Spring, but I do exercise the key when I work on the car and so far so good.
This treatment is a possibilty before doing anything more extreme. No guarantee that it will work and it may blow contaminants into far corners of the mechanism but before replacing a tumbler it is worth a try. I don't pretend to be an expert but if you don't hear the clunk on removing the key it seems to me that indicates a problem in the tumbler not the electrical switch.