Where did you get the sensor from? Lots of people will sell them as 'oem' and in the small print you find out it's 'oem replacement' or 'oem standard' which is only the same as when every supermarket claims to use 'only the finest ingredients' in their food.
The way it 'sortof' works with a new Crank Sensor suggests that the fault lay with the CS, but that there's something awry with the sensor still. Is it still leaking oil from the cam covers? If so I'd say that wants sorting asap or you'll be going downt he route of a new DIS pack too. Get them done and you'll save yourself some aggro in the very near future.
Air suspension is buggeredEasy and pretty cheap. Pair of Brand New Bilstein shocks for under £80 on heebay at the moment, excellent quality I use them myself. And cheap n cheerfuls available for even less. Some perfectly fine used ones could no doubt be sourced from a member on here.
It's leaking coolantEasy fix, presuming it's from a pipe. Old rubber pipes to be expected on a car of that age. Again, good, used ones from Wanted section easily obtainable
Rear crank seal and maybe sump gasket are leaking So are mine. Summer job, so long as it's not losing a litre of oil a month put that on the back burner, get it sorted when you can.
cam cover gaskets are pouring oil down back of engine Sort this soon as poss. Genuine GM seals, will set you back something like £70, but will last, well, how old's this car? 15 yrs old minimum? You'll be on the originals, so these'll last another 15+ years. Easy job, really. Undo the plenum, take off the covers, clean them up, plop new ones on, reassemble. Do it in a couple of hours on a nice day, have an ale.
Autobox seems to have become very jerky Easy. Check oil level. That's the most likely cause. Takes as long as it does to change a tyre and about as easy. Car up in the air (but as level as you can) undo plug, check oil level, if need more stick some in

If it makes you feel any better my car started out 10 months ago as a SORN wreck, lathered in dust and cobwebs, since then I've done the following...
Exhaust
Exhaust heat shields
Cat converters welded new flanges on repairing old rusted ones
Wheels and tyres
DIS pack
HT Leads
Timing belt
Entire front suspension overhauled or replaced with brand new incorporating...
New wisbones refurbed with brand new GM bush, balljoint and Poly bushes
Droplinks
Track rods
Dampers all round
MV6 Springs
Inner arches cleaned, de-rusted, painted, stone chip protected
Brake calipers refurbished, repainted, new seals fittted
Discs and pads
Front hub
Steering knuckles and all other parts cleaned, ground to bare metal and painted satin black as per factory
All nuts and bolts removed, cleaned repainted silver
Brake hoses
Brake fluid change
PAS fluid 50% change
New plenum
All vac pipes replaced
All vac boxes tested
Drive belt
New ICV
Leaking fuel line repair
Bonnet and boot lifters
Plus some other stuff.
All that came in at just under £800 (Take off the dampers, springs and the cambelt and that would bring that total down to around £500) So it's doable, can be done cheaply, without scrimping on quality, and works out cheaper every week than everyone else at work for what they're paying on their HP on their brand new cars. I've got just mainly cosmetic stuff left, no FM, some rust to be sorted, plenty of cleaning, tatty engine bay, back brakes to refurb soon as I can, but all in all she works, goes, stops. And does that with cruise control, climate control, heated seats and a smoother ride than any other car you can buy new today.
There's a few - a very few - 'Omega killers' - sort these very simple and often cheap issues out as preventative maintenance and you'll have a very good car for as many years as you want.
