All good info submitted already as this site has a lot of experience to offer help to its members for sure. This could be as easy as a bad plug or wire but the whole picture needs to be checked. The
oil consumption is a real clue so jump to mechanics of that cylinder. I do not think just a bad or missing valve seal is the culprit but maybe a bad valve guide, leaking intake gasket or poor piston to cyl. wall sealing would allow the amounts you are seeing (again you said no external
oil leaks so it is burning the
oil)
Do a simple vac. gauge test and look for a fast flutter on the needle for guide test. Do a compression test to check piston/cyl. seal with a leak down test if needed to isolate issue ( you can hear were air is going ). I skipped the simple bad wire or plug or even carbon tracking on distrib. cap because of oil consumption as reason for just 1 cylinder being fouled. The leak down test tells you more for cylinder mechanics but a leaking gasket or bad guide will not show up as quick with a leak down test. The Vac gauge reading with all the parts moving real time takes you through the different loads/side-loads imparted on things like the V. guide. You did not mention if you had oil contamination in coolant, check for milkshake in expansion tank or rubber hoses getting soft or oil film on exterior of hoses.
Again the amount of oil this bad boy is drinking is what I am concerned about and fouled plug is just a symptom of real issue. I hope I am full of BS and a new plug wire makes all better.