FWIW....check the timing of the cams before you tear into the heads. Mine had low compression on one side (albeit not as low as yours, mine was 170 - 175). The cam timing was off on that side. Reset it and the compression came back to spec. Just a thought.......
I was actually going to check that. All this will be easier to do with the engine out of the car. I could theoretically do it with the engine in the car, but it would be a pain. The belts are are 7 years old, but I believe the tensioners are original. I was pulling the motor for a major anyways, plus it has a oil leak at the front of the motor. I was going to preorder the head parts, but I am going to wait until the motor is out for more diagnosis. With the headers off you can see the top of the valve and even possibly clean them. It's hard to see the valves with boroscope through the spark plug hole. You can use a mirror on the boroscope, but I am worried about it falling off and the 10mm spark plug hole is a tight fit.
Compression tests are not very reliable to verify that the valve guides are bad. Keep in mind that not ALL of those engines with bronze guides get bad. Around 20% are bad, not the rest. High oil consumption is the measurement, but the car also takes some oil depending on how you drive. According to the manual oil level should be checked every 800 KM (500 MI) even for a new car. That's quite often. Blue smoke can be an indicator as well.
Just going over receipts for my red car. Valves done at 17k mi in 2004. I guess sintered steel was used. Car now has 30k mi. This is what I meant by flange/ring. Supposed to prevent guide from walking. Image Unavailable, Please Login
It sounds like you convinced yourself that most of your problems are the guides and even though you are pulling the engine for a service if you don’t do them it will always be on your mind A agree that you need to find the problem with the 2 cylinders running or think I read you said oil burning there’s is a lot of ways to check and test but it’s up to the tech doing the job and you on how to proceed A good machine shop can do the job R&R guides, seals and lapping in the valves I would try to find all or at least most of the problems before hand Sent from my iPhone using FerrariChat.com mobile app
A good machine shop can also precision measure the guides in place after pulling the valves. Specs are in the workshop manual.
Update, I replaced plugs and wires and got the car running fairly well. I did pull the motor and looked at the bad leak down. The valves looked good, but the they leaked. Pulled the heads and they are at the machine shop. I am going to do the guides since its all apart(not sure if they are bad yet). It would be silly not to do them in terms of making the car more sellable (if I ever sell it) vs the cost. At the end of the day the added cost of the guides is worth doing in case they ever go bad in the future. At least I will sleep better. It will also get: -All new coolant lines -All new fuel connector lines -New breather hoses -Fuel injectors cleaned and flowed -Belts, tensioners -New cam seals -New rear strut mounts etc..