My Trigger Is Slow To Come Back Up After I Release It

Both of your suspects are real and they are worth separating, because one costs nothing.

An analog trigger returns under spring tension against a pivot. Two things slow that return. A spring that has taken three years of compression loses tension, and the trigger comes back more slowly and with less snap. Separately, the factory lubricant in the pivot dries and becomes tacky, which binds the movement without feeling gritty from outside. Your note that nothing feels sticky to the touch is exactly what dried lubricant feels like, because the binding is inside the pivot and not on the trigger face. So do not rule it out on feel.

The test result is the useful part. Compare the return time of both triggers and keep the two numbers. If the left is healthy and the right is slow, you are looking at one trigger's spring or pivot, which is a contained repair. If both are slow, that is normal ageing across the controller and a wider refresh is in order.

Order of work: clean and relubricate first. Open the controller, remove the trigger assembly, clean the pivot and the spring seat with isopropyl alcohol to strip the old tacky lubricant, and apply a very small amount of plastic-safe grease. Not oil, which migrates, and not a petroleum grease, which attacks some plastics. A tiny amount of PTFE or silicone grease on the pivot only. This restores a surprising number of lazy triggers.

If the return is still slow after that, the spring has gone and a replacement trigger spring is one of the cheapest parts you can buy. While you are in there, do both triggers, because the left is the same age and you will not want to open it twice.

One thing to avoid: do not stretch the existing spring to add tension. It works for a fortnight and then it is worse than before.