I'm struggling to find a solution.
To fit a cone filter inside the "tool box" the filter would need to be no more than 6cm long and 8cm diameter to avoid the battery, frame tube & battery holder. This seems small. Ont internet it usually doesn't have both dimension. If anyone knows a make of that size please let e know.
Similarly the frame, battery holder & battery, prevent a pancake filter being fitted inside the "toolbox" in it's conventional orientation. If I could find a suitable connection hose with a 90 degree bend and an offset pancake filter that is a maximum of 12cm diameter by 6cm depth, then I may be able to use the space inside the "tool box" cover. The ones I've found dimensions for are bigger in diameter. To fit them I'd have to remove or shorten the tab inside the tool box cover that I presume held the tool roll. I don't really want to do that, except as a last resort. In any case it would still need to be circa 6cm deep or less. If anyone has fitted a pancake filter inside the tool box on a B40/C15 advice/photo appreciated.
Alternatively I could try bodging up a replacement filter housing as I have the gauze, rubber ring ( that it seems to go in) and the circlip. Bess provides the parts diagram on this thread. I found pictures of the outer perforated cover that appears to be 50/50 hole to metal. I can make that. But I can't see from the diagram how the gauze sits within the housing & how much much space is left either side of the gauze to allow the appropriate air flow. If anyone can provide some pictures or provide some indications to assist it would be much appreciated.
( A full detached original air filter housing was on ebay before Christmas. it went for £12 ish & I bloomin missed it because I'm rubbish at that sort of thing and it locked me out when I tried to bid last moment .... V annoying didn't talk for a day or two.....which pleased some but annoyed my better half ! - I'm sure there's a 3D printing project here for someone who's clever like that)