Hi Jon

This not a problem that I have ever come across before, but sure others must encounter the same issue too.

I don’t know of any specific tool, but sounds like an engineering challenge of the homemade variety.

Not sure what angle your approaching, but maybe cobble together a garden cane with a sponge tied to the end to get some soapy water into those hard-to-reach reflectors.

Hope this garden shed approach helps.