Hi,
From a couple of other threads (“Most miles” and the “MKV Oil Filter cartridge”) back to this one as noqw I know I need at least one of these circlips: C.491
I had not looked for one as my engine apparently has not had one in many many decades. 
But now (as I didn’t have the Spare parts books with me) I checked the MKIV “Jaguar Service Manual for All Models” 1946-1948:
As my engine is #SL2199 PLATE 8. on page 28 shows this all.
So in that diagram / drawing the part I did not have (and still do not) is “84 Circlip on Shaft” and jaguar part number is C491. None of the usuals seem to carry it and I did now also ask Worcester Classic Spares UK, lets see.
Cheers!