A couple years ago, when I replaced the seawater pump, it came with an upgraded kit, instead of the original style. Looked good and I know I've had leaking gaskets on the old version.

I noticed this last year, but repeated the issue this year. Normally I don't go too fast with passengers/kids but when I nudged it over 60, I could see the light come on from the bilge pump.
Normally on the old version of the raw water pump, when a gasket or seal is gone, I'd see it pushing water out of the leaky spot. With the one piece version, I am not seeing anything at all. This was all replaced last season, and probably only have 40 hours on it since then.
There is one other through hull fitting near the transom, but I think that fitting would be out of the water when the hull is at speed.
Any thoughts on what other places to check?

The only other thing I can think of, is the inlet hose at the leg, but that's really difficult to see, and I would think the pump is creating enough suction that a leak in that area would show at low speed or when the boat is stopped also. I've checked the manifolds etc. Everything looks good.

I did not really want to push things and ruin everyone's summer vacation, so was trying to think of other ways to test this out of the water, before going out and breaking something.

When the boat is at speed, there's a significant amount of press developed on the raw water pump inlet hose from the ram effect.. If there's a loose clamp on the hose at either end, that would allow water to start filling bilge at speed, then stop when you slow down. I'd start by verifying the clamps are tight at each end of hose.. Buddy almost lost his Scarab due this hose popping off. I use 2 clamps (at each end) for this particular hose since it's so critical.

If you have the typical T style water cocks in block and manifolds check them very closely. I have a heck of a time getting a couple of mine to seal. I've actually had to cut seats and skin the knobs on a lathe to get a few to seal.