We have more in common than I thought - I have 2 wrecked knees, 2 bad ankles and a chronically bad back, gained in the same way as you! I had the same problem getting in and out, but a really kind chap from MSCC who was at a classic car event I attended recently showed me how to do it. Once you have the knack it is OK - at first I could not get my right foot in, or get anything out!
Mark
