Faulty Brake Fluid Level sensor cap

I am getting the brake fluid level low warning even when smoothly driving on the flat and even though the fluid is topped up way beyond the mark. I suspect a worn sensor cap internal connection. JLM808, now DBC2241 (?) seems to be no longer available. Has anyone successfully serviced this part. NB: No fudging of the light please! I value its safety utility!

Its been a while, but I think one of the aftermarket manufacturers includes a new cap with their replacement master cylinder assemblies. I recall specifically looking for this because I also found replacement caps to be NLA.

Thanks for that reply. I have found a source in the UK and have ordered!