i will also add that most engines that have poor valve seal normally have tired valve springs.the hp500 is famous for this because they use a valve spring that wears out usually between 200 to 250 hours.i rebuilt a couple hp 500 efi engines recently ,i don,t know what they had for hours but both engines had several broken valve springs.the ones that were not broken were ready to break.

If the price is reasonable I wouldn't pass on the boat based on the leakdown check. 303 is a solid safe hull, and will take a beating. I know this from experience. Head job isn't too expensive when time comes for that. I'm thinking you could probably run it for a while based on the driving habits you posted.

Hopefully this youtube video can be opened up here for viewing. I have noticed that in the past couple of weeks they do not even show up in the threads for linking up youtube videos.

youtube video here if one can see it and open it up. ----- Anyways Dart and Reher Morrison will disagree about a leak down test is the test to perform only. How I know about this video and class --- because I was in it personally and the topic went into more depth than shown on the youtube video.

IMO both tests should be performed. Compression and leak down testing. Neither test is 100 percent that the motor is great to go. If one had a broken valve spring and or a very weak valve spring(s), leak down testing can show good. If one had a broken rocker arm - a leak down test can show good. I have had this before and were compression tests shown bad numbers but leak down tests shown good numbers.

I just was told that they did a compression test "sampling" of cylinders with different leakdown percentages. The compression numbers seemed ok to me.
The Port motor, #8 = 130 (20%), #5 = 128 (25%) and #2 = 125 (30%).
The Starboard motor, #8 = 140 (12%), #3 = 135 (25%), #5 = 138 (15%), #2 = 135 (25%).
FWIW.

Compression means very little as lots of people have already said.it basically just tells you if it has enough to fire.
Leak down is a true indicator of the engines health

If you like the boat go ahead and buy it just keep in mind it's either going to need springs,A valve job or new rings.

I would agree with this. The springs get worn out and no longer control the valves very well. This typically causes wear on the seats and valve faces. Most of your leak down is going to come from the heads. Very little is typically from the cylinders themselves unless you have rings that are broken or bores that have rusted and become very out of round.

you say this like you have one or are a powerplant guru

You say that like you already know the answer...........smartazz. Not even close to being a powerplant guru but I have spent some time beating on a Formula. Right?

or all of the above.

More than likely top-end related on the one that’s lower; very typical of the 502 MPI. The exhaust seats start to go away. Use it as a bargaining chip. 527 hours on the short block is nothing unless it hasn’t been maintained or had the bejesus beat out of it.