Well thanks to Karol of the Slovak Ariel Klub I now have the parts to put the crankshaft shock absorber back together. Here is the illustration in the parts book:
I think that what Karol has designed & manufactured is an adaptation of what Ariel designed. What is shown in the parts book as A6/712 (the 'sliding member') fits inside A6/715 (the 'spring retaining collar) which was possibly easier to make at the time. What Karol has provided I think is a combined part including the features of both of these parts as shown on the left in the picture below:
There's not much more to say about this bit other than that until I bolt it up finally we will leave it as it is.










