I did everything that you have done, no luck, still occasional skip. I noticed a correlation between skip and speed so i put a servo control on it and slowed the machine just a bit. Voila. No more skips.
There should be a slot in the end of the screw. Secure it with a screwdriver before you turn the thumb wheel or else the entire thing will try to turn and rip the membrane.
Yes. Try to force water thru the port on side of boat first. Crossing fingers....
Personally i would shut off seacock and remove hose from water pump. You wouldn't want to have anything plug the pump or get stuck in strainer. Easy enuf to vacuum water from bilge.
Water is plugged, hopefully it's the hose. Disconnect hose, attach garden hose, blow it out. Consider barnacle buster or similar after you get water flowing.
Or you can force water thru port discharge and maybe it will back flush.
Contact the surveyor. Let him know you are interested in boat and are considering another survey, by him. See what his response is. A good man will have a good response.