It's been awhile since AX4N's have been in production, So I'm guessing the gasket is at least 20 years old.
I can't think of any issues with all the 4R70W, 6R80, 4R100, 5R110, 6R140 gaskets I've reused over several years that weren't 10 years or more old or had a ton of miles.
Ford didn't stamp "reusable" on the pan for your benefit, They don't want foot the bill for new gaskets under warranty when they can be reused 99% of the time during that time frame.
Your vehicle....Your decision, Makes me no difference, But you're advocating RTV is a better way....I disagree & think it's pretty hack thing to do when both Ford & GM explicitly state to not use RTV on their units AND engineered some high quality gaskets that may not be 100% reusable in perpetuity, But still a big leap from Resin/Fiber/Paper matrix, Cork, & pure Rubber Gaskets that were once the norm.
Resin/Fiber/Paper matrix pan gaskets actually worked quite well when installed correctly, ALL 4L60E's had this style from the factory. After a couple heat cycles, The resin in the gasket activates & basically glues the pan to the trans case. The issue's are....It's not at all reusable, The pan bolts are easily under or over torqued, And the pan is easily distorted if the bolts are over torqued.
Yes.....Some units call for RTV to seal the sump pan (Lots of Chrysler & some Toyota/Aisin units), But the pan flange design is different if you've ever noticed, Has little reservoirs for RTV between the bolt holes.
And a personal issue I have with using RTV......I have to clean up that mess more than I should have too, RTV jammed in every blind bolt hole & Dried RTV all over every bolt eats up time I could be using to diagnose & repair things. This goes for anything where RTV was used for the wrong application. Like Coolant O-rings, Oil pump housings, Using both a gasket & RTV.....Though there are situations where surface imperfections or pitting makes it necessary.