I fried my exhaust valves by 26k miles but started having problems by the first valve service...this is not normal...then they began to fail again at 52k miles...it's been a very long road getting to the bottom of it...long story short; I use to engine brake everywhere...every stop...every chance I could...this was pulling oil into the cylinder and not completely burning off...it made a mess of everything in the top end...So you are trying to tell me it's not normal and posibble cause is valve mechanism worn out or valves need adjustments? . BTW it's 17.5k miles
I've backed off from using it excessively...and stopped completely around town...but I'll still rely on it banging around in the twisties...I've been walnut blasting my intake valves every 9k miles or so which has worked remarkably well in keeping the valves from failing..havent had to go into the motor for over 40k miles..despite a few scares...if your not experiencing the really loud engine braking I'm describing a can of Seafoam followed by one and done should help stave off any engine surgery...it never completely cleaned the valves but did get the exhaust valves seated and silent again...other than that seek out Exxon gas when convenient...techron...I use engine brake too. If I stop using it should help or not really?