Pax,
That would be all well and good if the BBMF aircraft were being 'worked hard and put away wet', and if they were subject to the rigours of a wartime environment, and wartime servicing, out in the open.
Except that the Spitfire and Hurricane were never designed to 'last months' in the way that (say) the Bf 109 was, and were designed to be as rugged and as robust as it was possible to make them.
And then there's the fact that these aircraft have been stripped down and rebuilt using an astonishing array of new parts - in many cases today's flying Spits are new aircraft built around a genuine data plate, and with original parts used simply as patterns.
They simply aren't the creaking geriatrics that you imply (unlike some of the posters on here).
Moreover these aircraft are minutely inspected - frequently, and are subject to a 'no expense spared' maintenance and overhaul regime that means that every part that can wear out will have been replaced - probably several times, and that parts that are subject to fatigue will be even more carefully looked after.