Valve seal? Did he mean the valve cover gasket? $100 for parts and labor for valve cover gasket and PCV is not too bad. Pretty much the going price for that sort of repair work - as the parts are very inexpensive, but that job is pretty much all labor. Curious - did he replace the spark plug wires, replace the plugs as well?
1 quart every 1500 miles is not too bad - I've seen much worse. Might see some benefit from running Valvoline Maxlife High Mileage motor oil - as your oil consumption hasn't crossed over to the point of no return.
Sears convention motor oil is made by Warren Petroleum company, same company that makes Walmart's convention motor oil. Its an OK oil - but does tend to shear down quickly, get burned off more easily. Probably why you saw a marked difference when you added the Lucas additive.
As for treatment - impossible to say. Some cars respond well to running a different brand of motor oil, some can do a piston soak and have no problems. Some cars don't respond to anything short of a complete engine rebuild. Problem is - not every 8th gen has this oil consumption. Some have twice as many miles as you and don't burn any oil. Some have 1/2 your mileage and burn a quart every 150 miles! I'm convinced that much of this discrepancy is likely do to how the car was originally broken in and what oils were used during the first couple thousands of miles of operation.
Best you can do at this point is to monitor the oil levels closely and often. Every time you fill up the gas would be just about perfect. Always keep additional reserves of oil in the trunk of the car, to top off as needed. Must keep the car from running low on oil at any time - if you find yourself having to add 2 or 3 quarts of oil at once to bring the levels up, you've waited too long and potentially worsened the rate of oil consumption.
By keeping up on oil levels, you can actually run the car a surprising long time. Some owners have been able to drive 10's of thousands of miles / years of driving even with excessive oil consumption. But eventually, it will come to a point where no additive, no amount of oil top offs will be cost effective. That point - you'll have to rebuild the engine, do an engine swap, or just dump the car.