Well Lee, that doesn't look to dissimilar to how mine looked when I picked it up in late 2012 from someones backyard. Mine is circa 1996 and my approach when I got it was to... do absolutely no cleaning at all
Mine rotates ok although it does have one slight sticking point that
could play havoc with a motorised system?...I'm manual push to though
Personally when I ever get around to cleaning mine I recon good'ol warm soapy water and rinse off with a garden hose would be perfectly adequate
Of course after the good clean, a close inspection of the fibre glass should tell you pretty quickly if it is going to crack and leak, or not..?
Good luck with the project
Mike