No clamp on water pressure line, SHop denies responsibility. Help!!

[Corrosion]

My repair shop changed my water pressure gauge (2005 150 Yamaha 2stroke) When I picked it up, shop said water pressure gauge line was clogged but he cleared it out. Gauge failed again one or 2 trips later. Indicator showed water pump was working so no worries. Next day it started running bad, not getting on plane. Sat 8 weeks then taken back to shop. Shop diagnosed that SOMEBODY failed to attach the water pressure line at powerhead with a clamp so it was spewing salt water over motor and sucked into intakes, so there is corrosion inside cylinders, and on external components. My water pressure line hose has markings showing that it previously had a clamp. No other shop worked on it so clearly my trusted mechanic failed to put the clamp on. When I pointed out that he is the last to work on it, he changed story, said he only worked under console, not under motor cover. Not sure how you can clear out a line that way. CAN ANYONE PLEASE PROVIDE ME WITH PAGE FROM REPAIR MANUAL SHOWING THE PROCESS TO DIAGNOSE AND REPAIR PRESSUER GAUGE AND/OR UNCLOG THE LINES. I spent $4700 to have a rebuilt powerhead installed. 'Im taking this to small claims court, no attorney, worth a try. Any help you experts can provide is much appreciated.

[99yam40]

nothing in writing? that sucks
probably just shot air thru and blow line off
voice/words are not recorded

make sure you ask where the plug was that he cleared