916 misfire

So out for the wife on Sunday and the 916 starts to drop off onto one cylinder.
I thought it may just be because I was going slow, but an Italian tune didn’t cure it!

Back home and I noted a couple of drips of coolant on the rear cylinder by the exhaust.

On taking the plug out the rear one was a darker colour than the front and the cap (the part that fits on the inside of the cylinder) had condensation. Almost as if it had been dusted with an atomiser.
The inside of the cap showed signs of the contact rusting.

So swapped the plugs front to back and closed the gap on the cap contact, a good clean of the plug recess and a squirt of WD.
All good running as it should again, and a 40 mile blast just to confirm.

Now I did give it a clean the day before and hadn’t ridden it so that may play a factor.
But the question for the learned is failure of the rear cylinder gasket a known issue?
Can you get away with tightening the head down?
If not can I replace the head gasket with the engine in the frame?

Had a rear Cylinder base gasket leaking a bit of coolant on my 916 Biposto some years ago.
Got it replaced while in for a sevice.
I will do most maintenance jobs myself, but I don’t have the engineering experience to play with the inside of motors, so I pay someone who knows what they are doing.

Head gasket replacement with engine in frame? - Probably, but I bet it’s a right pain in the arse.

I have just worked through the water leak and misfire on my 99 ST4 (916 motor) . Every time I went out for a ride I found coolant collected in the ridges behind the rear cylinder and splashed on the hugger.
I looked everywhere for source of my unwanted water feature to no avail, I have not owned the bike for very long and had only ridden it 4 times! On the last ride prior to strip down the water feature was gushing as expected and the intermittent misfire developed in to something awful; I surmised that the two things were connected and perhaps coolant was both escaping and getting in to the combustion chamber of the rear cylinder.
Once home, as the bike cooled down, I stripped it down, I was getting to be a dab hand with the fairing removal procedure (that was not going back on until the well ran dry!) and cam belts and cam timing, after all I had only fitted them two weeks ago! Then comes the real fun removing the cam belt idler and adjuster, exhaust, throttle, bodies , etc etc finally one is faced with the top comedy cylinder head nuts. In a past life all four of these 15mm a/f darlings had been heaved up to the limit and beyond by some knuckle dragging superstar, in a desperate attempt to stem the flow of coolant. After much grinding of a 15mm spanner a make shift tool was crafted that promptly snapped! After much grumbling and tutting I found a much modified Britol Whitworth spanner that fitted perfectly and all was removed and cleaned. I handed over £55 to the helpful chaps in Winchester for a cylinder base and head gasket and a few o-rings and a tube of gloop. Carefully assembled the scattered components, poured in the coolant turned the key pressed the red button and off I went for a test ride (sans faring).
Happy to report the leak was fixed but the misfire was still there(bugger) pulled up, prodded, poked, wiggled all things nothing changed (why should it) however noticed that misfire changed as I lent the bike on to the side stand, then improved slightly as I picked the bike up straight! Something fishy going on here! And I need to find the fish pond!
Headed home on one and a bit cylinders removed the seat, prised the aluminium lid from the ECU and found it was awash with the stuff that fish do all sorts of things in! Removed ECU, stripped out everything including the mucky brown water (must have been very dirty fish in there) washed all components in WD40 dried with hair dryer popped in two 4mm drainage holes for good measure assembled all and tested, pleased to report that the old thing never missed a beat. problems solved!