A further update, & for general information; not only do the correct number of teeth have to be specified, (32) but also there are two lengths of shaft available for the Wheel Box! The correct length to suit the Roadster is 65mm, this turns out to be the same as fitted to a TR6.
Replacement fitted today; www.angclassiccarparts.co.uk; now have three working wipers, just in time for this weeks MoT!
Thanks for all the replies & suggestions.
