If the struts were leaking it would be pretty obviously oily I suspect....
Changing the spheres is pretty straight forward, I managed it with just a Haynes manual, half a day or so but anyone competent could probably do it quicker!
Only 'gotcha's' I recall was the studs on the new spheres weren't threaded to the bottom like the old ones so I needed washers for them...
if the short pipes are corroded it might be worth replacing them, pretty cheap..I think the big ones are a bit more though...
access to the spheres is through the passenger compartment floor, took me a while to figure that out..
To check the system moves - which will show if the rams are seized - you need to load up the rear of the car, enough to make it sink...then start up and run it up to 1500-2000 rpm or so, should start lifting back to normal ride height fairly quick - a minute or so rather than seconds
You could try getting underneath and twisting the lever from the swaybar to the valve..but you will want it to be on nice high ramps,cos it comes down real quick if you turn it the wrong way......ask me how I know...