The valve seals keep too much oil from going down the valve stems and getting burned in the cylinders.
The valves themselves seal against the seats in the head - that's what allows good compression.
Two very different parts of the valve, stem seals vs. valve seating.
Worn valve seals are very likely in this. They can be replaced. The dealer doesn't want to diagnose this, because it's a lot easier to replace the entire engine than to go down the path of "well, valve seals didn't work, so, let's try rings" and you get all upset at the cost.
How mechanically inclined are you? Got any buddies that can do a valve seal job? I would start there..
Forgot to mention. I've helped build a cpl motors as a kid. Fairly mechanical. I've changed VC half shafts do my own oil changes.... never done breaks but have help a few times and know I could if I had to. Fixed washing machines and dryers...
Just moved half way across the country and dont have friends yet, lol. I have family but they count on me to fix thier stuff.