M5A1 Stuart - Radiator cap part number or cross-ref number.

[Needle]

Hi all. When doing some major work on the Stuart, it was discovered that one of the radiator caps is broken (It just fell apart when released.) There are no markings on it, (or the one fitted to the other radiator), and I cannot find the part number in any of the manuals. (it probably staring me in the face, but I just cant find it!). Does anyone know the part number or the number of an equivalent?........................or does anyone have a spare one that they would like to "negotiate" on. Thanks.