yes the pushrod, could only see it if I twisted it.. not visual just by look at it

The 8.1 is not adjusted like in the vid.

From manual 30
Not sure its an exhaust issue. Can pressure test the man by sealing of exit port and apply pressure to intake port

I would lean toward removing the head and have if looked over by a machine shop

Johan, I can see you have some bad luck here! I think you have to pull the heads and have your valves done. That´s what I did after my CMI misshap, had similar bad numbers but at #7 and 8. Do a new leak down test first as AllDodge wrote to check the rings.
I changed both my low- and high pressure fuel pumps a couple of years ago, I didn`t take the housing of the pump out just took the lid off and then the filter and the pumps. The colour inside my pump was intact, looked like new. It was a little tricky to get the lid back on the pump if I remember right. My engine is a 2005 with 550 hours on it now.
If you have the 425HO standard cam I doubt you have reverison and I have never heard or read here that anyone have had reversion on this engine.

Oh, thank you. Is the valve adjustment just different on the marine 8.1L or is it 496 in general?

Do you mean pressure test it like I trying to describe on the picture below or on a different way?
Feed the intake port with water and stop it after the manifold before the riser?

Yes, wonder when the good look will come 😂

Im going to take of the heads.
But first I must take the valves/rockers of right?
And after that the intake manifold before I can take of the headers?

First time im doing this.

Did you also have problems with reversion due to bad valves or did it happen after the cmi leaked?

I have the leak down test tools, but not a compressor. See if I can borrow one.
But I can do a leak down test with the valve covers off right?

Did you manage to get the plastic box off that is surrounding the fuel pump? I have tried but I didnt make it, gonna try again.

It should be the 425 HO cam on it, I hope.
A mechanic shop here in Sweden rebuilded it from a 375 Mag to a 425 HO.
I have also read that it shouldnt cause any reversion with the standard HO cam.

Yes, pressure test man as shown

There are several motors which valves are adjusted by torque to spec.
The vid is good and there are also several which are adjusted to zero lash and then 3/4 to 1 turn more. Just depends on which motor (year, serial number). Always good to have a service manual

I will test the manifold as shown.
Just with the garden hose I think/normal garden hose pressure from the house?

Okey, I see

Best to test with air. Air will leak where water may not when cold. Test around 2 bar

Okey, so test it with a compressor/air.
Spray water on it and look for bubbles or put it down in a bath of water maybe 🤔

The torque to spec net lash adjustment was copied from GM's LS platform for the GM 8.1 platform. Mercury sourced GM longblocks for their 496 mag/HO. The HO cam should not cause reversion.

Heads will need to come off, pressure test, cleanup, Valvejob hopefully will fix them. Leakdown test the cylinders to be sure thats your problem.

Your exhaust manifolds see roughly 20-30psi h20 during operation. I would not be afraid to double that number with air psi to test. Use air as mentioned and submerge manifold into tub of water. Bubbles will be very noticeable.