Replaced gasket on moka pot and it misbehaves - should the gasket be treated with anything? First of all, I've seen Why does my moka pot sputter?, which covers a very similar issue but has no answers and doesn't ask the specific question I have.

My 6 cup Bialetti is probably from the 1960s, but the modern gasket still fits and I've replaced it before (over 10 years ago, but I don't use it daily). It was blowing steam from the screw joint so I checked and replaced the cracked gasket. With the new one, I get about a teaspoonful of thick coffee before the sputtering (that normally marks the end of the brew) starts from the tower. If I leave it sputtering I eventually get a little less than I should, but enough to drink. I don't normally tamp it, but smooth over the grounds with the back of a teaspoon before wiping the sealing face of the basket with my hand. I use a very small gas ring, with flames smaller than the base (a little smaller to start, reducing once the flow starts). 

Assuming there were grounds caught in the seal, once I took the seal out and cleaned it, before assembling wet. It behaved much better, but only that time. I normally only rinse the pot (it's very well seasoned) but I'll give it a good scrub before I next use it. I wonder if the seal doesn't seal very well dry, and whether wiping a thin layer of neutral cooking oil over it would help. Is this a good idea?
It sounds like you know your Moka pot well, and it is true that it is an easy way to get deliciously strong coffee. That being said, it can also be very nuanced in how it works. First, your new gasket should seal perfectly well and as long as there is no sputtering from the screw joint, it is good. 

Sputtering means that you are forcing too much steam too quickly through the grounds and into the pot. Try using a high heat to get the coffee flowing, then adjust the heat to keep an even flow into the top chamber. It's possible that with a bad seal, extra pressure was being release from the screw joint and now it is all being directed through the "tower".

Hope this helps!