Has your windscreen washer bottle disappeared, or just disintegrated with age? This plastic washer bottle for early Minis with the Tudor logo has a 2" neck size, with internal tube and non return valve.
For originality see
17H2536 originally made by Winguard which had correct size smaller neck as fitted to the MK1/2.
A new stainless steel bracket to hold the bottle is also available as
37H9712 or for original brackets see
37H9712ORIGINAL.