I wouldn't do it unless completely disassembled. Lemon juice is an acid and you wouldn't want any residual acid left in the shaft pivots and other critical places. It will also wick into any installed screw threads and you could never rinse it out of these places?
I doubt if it would hurt rubber or plastic as long as its not too hot, but you have to be able to rinse it 100% or its still active and at the very least will cause corrosion in threads and whereever its left behind.
Some poeple would try it but not me, .. there's only one right way.