If it is earwax that is causing his ear to be stuffed, Debrox is the way to go. Recommended by many docs I have worked for. The thing is, you usually have to put the drops in for 2-3 days to soften the wax build up, then use the bulb syringe and warm water to flush out. It can be a little messy, but does the job.
That being said, if he hasn't seen a doc for a while, might want to have it looked at, or at least give the doc a call and explain the problem and ask what you should try.