Hi there... Okay I started this 5 times... Then rebooted my computer as there was clearly something the matter with my touchpad or keyboard. Anyway...

Tam is right Aspiration can be caused by a poorly functioning epiglottis. This is often caused by damage from radiation... However, he should have a swallowing test to determine he exact reasons. Sometimes an adjustment is all it takes to fix things. He's only 4 months out. Being older, and this being his second time around it will take longer to heal.

My father in law had his esophagus removed and stomach pulled up to become a new esophagus. He has no sphincter at the entrance to his stomach where there should be one, so he was getting a lot of aspiration, (related to gastric reflux) His swallowing is fine, but he was still aspirating. There were a few techniques offered to him to help him with this that have all but solved the problem.

What I am saying is there may be ways around the problems he is experiencing. Being on feeds it could be that he is getting a bit of reflux as well. This can also cause pneumonia.

Maybe slow down his feeds and run them on a pump overnight so he is not tethered to the machine all day and gets the bulk of his nutrition overnight. (this will go a long way towards making him feel normal by allowing him to move freely during the day).
Getting up and moving will help him as well.

ultimately take him to have a swallowing test done. Find out exactly what is going on. I know how you feel - my father in law was a right mess after his surgery. sometimes it just takes a bit longer. Radiation has far more impact than surgery.

hugs.