I've been playing around with a couple of rotary switches that I bought off ebay. One is the original style (39156) 3 position switch, but that needs a external relay as used by ERA to get the self-park. The other is a Rover P6 wiper switch with 2 positions, plus a variable sweep position. This switch also has a press function, originally intended for washers.
I don't have washers on my car, so that feature was surplus to requirements. However, the three rotary positions don't allow for self park, so I decided to try using the washer switch as a "press to park" function and I'm pleased to report it works fine.
Position #1 is OFF, position #2 is high speed and the 3rd position provides a variable slow speed. Turn the wipers of and they stop at the position they were in when turned off. However, a brief press on the knob and they will self park.
Not exactly as original, but it looks right and they self park without the need for fancy relay boards. Result.
Paul