I have had a Vermont Downdrafter since the 1980's. It has done everything you listed including the top draft warping and not closing properly. I had it repaired twice over the years by a local fabricator. He replaced the draft plate with heavier stock and welded the corners of the opening to stop the box from warping. It seemed the plate would go out of shape with one corner becoming elongated not allowing it to swing back into a closed position. The first time it was repaired the material used was the same gauge as the original. It lasted a good while but eventually did the same thing. The new heavier plate works in all conditions and shows no sign of the old problem. A larger diameter steel rod was used to weld the heavier stock to.

The side L plates are cast iron. After 30 years they were badly out of shape. I took the best one to Columbiana Foundry, Columbiana, Ohio. They cast 5 new plates including being able to cast in the cutouts for the mounting bolts requiring no machining. The cost was very reasonable and I now have a pattern for future use. The new plates bolted right in with no adjustment necessary.

Our floor plates have never warped or burned through. I am sure the foundry could make a new set but they would require some machining to sit flat on the rails.

Our stove is in excellent condition. The design is now a classic. I have not found any free standing stove on the market today that takes a 24 inch log. Anything that large is a furnace add on.
Every year we disassemble it taking out all the ash especially from the pocket by the upper vent plate and replace the cracked and broken fire brick. We get the firebrick from Brunks Stoves in Salem, Ohio. Our unit still works like the day it was made and has no trouble keeping our 2400 square foot home in the high 70's and 80's even in subzero weather.