Hi Pete,
I can just see you roto-rooting with the wire! This is good advice regarding the PEG it does not make any sense the get a smaller one. I managed to get mine (pencil size) clogged several time with vegetable pieces. Using a 50 ml syringe and water had 2 different effects. A) It cleared the obstruction and you got a very sudden bolus of water directly into the stomach or B) a very wet face....

Since your peg was leaking after the feeding you probably also have acid on your chair. What my help is mineral water/detergend and wet paper towels (several rounds) followed by dry paper towels to wick away the liquid. After the stuff is dry you can probably use a stiff brush.

Best
M