2001 s 430 airmatic
 

for past few yrs if car got below freezing driver rear shock would go down but back to normal when above freezing.
in past few days both rear shocks drop in an hour or so and the front ones slowly after
pump works and I can drive. how can I tell valve block vs individual shock? If one rear is bad will all go down? Is Arnott still the best? Is DIY easy thanks