Get rid of those flip flop wipers by renewing the wiper drive gear.
Note particularly the white nylon park switch activating piece on the drive gear.
This may be worn on your unit and the park no longer works properly.
Make sure you check this is correct for you by counting the teeth on your old one.
As fitted to many vehicles including: Fits many British Classic cars including:
Classic Mini Mk2, Mk3, Mk4 MGB MG Midget (Late 1275 and 1500) Triumph Spitfire MK IV & 1500 Triumph 2000 Mk2, 2500TC, 2.5PI, 2500S Triumph GT6 & TR6 Range Rover Classic (rear wiper) Land Rover 90 / 110 / Defender to 1991 Morris, Austin, Leyland Mini Saloon and Van to around 1980. Range Rover rear wipers etc. Triumph