^^ my first thought were who changed the oil and if there was 7qts added to begin with? I say this because that would put you at 5qts. If your buring 1qt every 3kmi, that would get you down 5qts in the end.
I would say that valve seals is NOT your problem but rather rings. I'd reccomend having a leak down test and compression test done, but def a compression test. Maybe you have a dead cylinder? A plug check would verify a dead cylinder but not a leaky one.
If you had a cracked head or gasket issue, you would have coolant in your oil just the same as you would have oil in your coolant.
I doubt Synthetic oil is your problem. If it was to be burning up as you think, pull a plug and see what it looks like. If your oil is burning up, you'll have ash deposits on your plugs. Generally speaking...Synthetics have a higher burn temp than conventional so most Synthetics will burn LESS than conventional oils.

Regarding your oil change intervals. Just because the oil is Extended service doesn't mean you can go 12kmi w/out any service. You should be changing your oil filter every 6kmi if you plan to run the full 12kmi service intervals. This helps remove all contaminants that would otherwise stay in the oil for the entire duration and prevents clogged fliters to improve oil flow. Even the best oil filters such as Mobil 1 or Pure One don't have the capacity to properly filter for 12kmi. So, a filter change and a top off should be done at 6kmi and you should be checking your oil color and level every 3kmi.

i would think the low oil light would illuminate at the point of only having 2qts left. I would look into the sensor and make sure it's working. otherwise replace so to warn you for the next time.

 

I agree! I check mine once a week or so just for fun. None of our vehicles lose/burn oil at all, including the Camry at 125K.

 

I have always run synthetic oil and I have never had this kind of trouble, it sounds to me like they might have short changed you when you got the oil changed, I know it is little to late but when ever I get my services done as soon as I get home I double check everything that they did and not just because it was a free service but just for piece of mind.

 

I'm thinking you got shorted last oil change. I would just check it each week. I use M1 from new and check mine every fill up. Keep a rag under the hood. Throw back to the old days. Besides gives you something to do while it fills. Also, I change mine every 6k. Good luck.

 

Sometimes when an "oil changer" is not paying attention the gasket from the old oil filter can get left behind. They then tighten a new filter over the old gasket. It will leak slowly if thats the case, so check around the filter.

 

Great info DD!

 

like everyone else is saying just keep your eye on it for a while until you feel safe with and if you are still loosing oil somewhere then you are going to have a compression check done.