"Probably a silly question, but what are the pros and cons of air Vs
Nitrogen filling of the oleo struts."

The only problem with servicing a strut with air is the source of the
air. Many shops have an air/water separator hook up to the compressor.
Some shops don't and you tend to get a lot of water maybe lots of
water in the strut. If you live in an area that gets cold the strut
will freeze due to the water. The water also causes pitting on the
strut crome causing it to cut the seals and leak more.

Nitrogen does not cause the seals to rot and crack as fast as air.
Also some maintenance manuals call out to use nitrogen in their struts
and other air. No water in the sturt is good. If the seals are good
and the strut is not pitted it will or should not leak.

Stache