I also suspect a blocked strainer. Priming trough the outlet generally gets things going again. My V288 was constantly loosing prime, and had to prime regularly as described. Quick to do at my dock, not so simple when away from home base.
One day I decided to inspect the pump after running the AC for 15 minutes, it was running hot and making more noise than I would have expected. I aquired a new pump, took me 2 hours to install and now it works perfectly. Surprisingly, it now actually self primes, I have taken the boat out of the water a few times since installing the new pump and never needed to prime the AC as before.
With the old pump, I noticed on 2 occasions, after hitting large wakes at high speed that lifted a large section of the boat out of the water that the AC would require priming whenever I used it thereafter. Note: The AC was not running while underway at high speed. I suspected that it lost prime due to the inlet being out of the water. Has anyone else experienced this?
You more than likely know this, but these pumps are generally not able to draw water without having water in them, it needs the water to create suction, loosing prime means the pump is drawing air and unable to draw the water. When you prime it, you fill it up with water to get it going. My apologies if I am stating the obvious, but not everyone is familiar with how these pumps work.
Hope this helps.
Regards.