At that age & mileage it's a sure bet they need replacement; no further diagnosis required.

The 124 shop manual says the struts need be replaced only if they leak or make noise. They don't wear out with normal use. I presume the accordian boots on yours are pretty well shot? It'd be nice if those could be replaced to protect the expensive shocks, but I don't think they are available separately.

The shop manual specifies the acceptable range of pressure within the nitrogen spheres. I don't recall the numbers, but it's extremely high. I suppose they could be tested, but it would require specialized equipment. Citroen automobiles use an essentially identical hydropneumatic suspension and it's common to recharge the spheres. Many moons ago I had the number of a business which did this, but have long since misplaced it.

How is foam a sign of bad accumulators?

- JimY