Listmember Ed M. originally turned me on to this simple procedure, and recently it appeared in the Facebook Vanagon Owners Group, so thought I would share again.  Yeah, on a Tintop you adjust seat to most upright, slight forward on rails, at end of travel pull up the safety catch, continue sliding forward and off.  Lift off, rotate, slide back onto rails--works like a charm!  I recommend thorough cleaning of seat rails while it is off, and then Vaseline for lubrication (doesn't stain carpet which invariably will be contacted by seat rails).  Sure....I would be willing to buy a swivel, but this raises seat by 1.3 inches (Westy seat cushion is thinner than Tintop seat cushion for this reason); and finding an available Westy seat in my color and great condition is almost impossible.  This DIY method works just fine.