Just to be clear, the wipers arms I have illustrated above are completely different to those fitted to the centrally mounted suction wiper - see https://www.triple-mregister.org/forums/topic.asp?TOPIC_ID=18881 It is these that Willie Mackenzie will hopefully be reproducing.
Edit. George, L2004 had the strengthened windscreen. Simon J J3437
Who can say when the switch from the earlier to the later J/L2 windscreen supports was made? I reckon the works might have used parts bins to assemble the cars, and during the process of switching could well have had bins containing both types of windscreens.
L2004 was part of a production run on 24th March 1933 - from chassis L2002 to L2010. 12 days later L2023 was part of a production run on 5th May 1933 - from chassis L2021 to L2032.
The factory file for L2023 does not contain much information but there is a worksheet which states:- "22nd August 1933 - in for various repairs - cracked windscreen - transmission snatch - de coke etc."
So it could well be the windscreen frame was replaced at the same time and maybe only the old style was in stock? Perhaps the car was in an accident thus the reference to various repairs. The factory records do show that quite a few L2s were at the works for accident repairs - as noted in my piece "L2 Magna - The chassis files" printed in the 2013 Yearbook.
Indeed who's to say for sure but there is a photograph of a J2 at the factory taken in late January or early February 1933 and it has the strengthened supports. So they were clearly a production line item by March when the L2s were underway. I’m not a subscriber to the ‘parts bins' explanation as though the cars were just cobbled together. - there was a production line and photographs show various parts lined up for use, suggesting a degree of production line organisation.
However, your comment about a cracked windscreen is perhaps confirmation that hanging an electric wiper motor in the middle was not a good idea. And also your comment about cars going back to the factory for accident repairs resonates as L2004 was back twice, its owner, Lloyd Cowdy, being referred to in internal factory correspondence as 'the wild Irishman'!