Nigel,
It looks like you've discovered the jacking strut. As for changing the filters, I wouldn't even attempt it without taking the top deck off. The hatch underneath Is just not big enough to do anything with, except maybe drain the water (which always seems to find a way into the engine bay) back out. The gearbox filter is even worse, especially in a Sabre where it is mounted on its side, right where you need it to drip oil over your steering discs and ensure you need to change the pads at the same time. Welcome to tracked armour
Chris