Out today and noticed a couple of anomalies from the gearbox

Driving at 45/50 on the flat and for a second or two it felt as if the car came out of gear. Without pressure on the pedal the revs rose without increase in speed, as if I had found neutral.

Corrected itself after a couple of seconds when revs dropped again.

A short while later driving at steady speed up a fairly steep long incline the box suddenly dropped a gear making revs rise sharply. This lasted 2-3 seconds and then corrected itself. Similar to kickdown effect but I was not accelerating or changing throttle position.

The car is 16 years old but has only done 56,000 miles so very possibly short or stop start journeys.

I know that the gearbox is supposed to be sealed for life but is there any benefit to changing transmission fluid?

Any suggestions welcomed

Yes, although sealed for life jaguar changed it and offer the service.

i read it's recommend at around 70k but as yours is well below that but 16 years down the line it'd be worth it. 

 

One note of caution though, make sure whoever does it uses the proper jaguar recommend ATF as "normal" ATF will wreck the box.