I'm sure no doctor, but as a patient who suffers chronic sinus infections, it sounds like you could have one too. The passages probably weren't opened 25 years ago when you had the nose surgery.
My sinus openings were opened, but all that did was give me a drippy nose all day every day, despite antibiotica, antifungals, sinus washes twice daily. My allergies are well controlled with shots, so it's not that either.
If you get temporary relief with antibiotics, like I do, I'd make a bet on the chronic infection (as a patient). Sinus washes probably don't normally get into the tiny openings into the sinuses. Mine are opened, but it doesn't help any. I suspect I have a plaque which isn't washed away by just a rinse. I've tried antibiotic in the rinse, but that didn't work either. Recently I was on Diflucan (for fungus, yeast), but that didn't do anything at all but give me horrible nausea to the point of stopping it.
I'm not sure what you mean by sinus plates. Usually we talk about the sinus cavities. The sinuses in the forehead drain down, but the sinuses in your cheeks drain upwards and therefore only drain when you lean forward or lie down.
My allergy doc tells her patients to rinse with 1/2 tsp noniodized salt and a pinch of baking soda in a 8 oz water.