Hello from Finland.
I've been a Mercedes owner for only a year now but some common air suspension issues have been very familiar to me, as my car is -04 E270 CDI Stw with rear air springs.
First of all, ten years seem to be quite normal life span for rubber air bladders so it was no wonder the left one already leaked some when I purchased the car. New Arnott springs cost around $600 for pair and were pretty easy to install. As far as I know, they are also designed better than original Bilstein springs, which have some certain flaws.
Anyway, after replacing springs there were still occasional problems with suspension; screaming red "car too low" errors, not so dramatical "visit workshop" errors and visually imprecise height adjust. So I took some time and studied the function of the compressor unit...
In my opinion the most common problem, especially in freezing conditions, is moisture. The non-Airmatic system itself is pretty simple and straightforward, containing only couple of solenoid valves, but only a tiny drop of water in wrong place may freeze and stuck one of these valves.
Mercedes uses the very same Wabco compressor unit as Audi, BMW, Jaguar, Range/Land Rover, VW and Porsche in their air suspension system, only some wirings and housing differs. This unit has built-in air dryer, which is defined as "maintenance free". In fact, it is very serviceable and also will need regular service to function correctly.
As everyone who owns any kind of air compressor knows, more or less moisture will be condensed in the bottom of the pressure container. Of course this depends on climate, but if you live in place where sometimes rains water and/or snow, your compressor surely will take moist air into it. If there are freezing days too, you definitely will have problems sooner of later without working air dryer.
This far I have seen only Audi's and MB's service manuals, and both says the dryer does NOT need service as the system purges dried air back from springs through the dryer and that way takes the moisture from it. The only drawback is, that dryer never works at 100% efficiency (takes same amount of moisture that it gives back). Furthermore, if there is any leak in the system, the amount of dried air is more than the purged air which should regenerate dryer.
The good news is that dryer unit has removable cartridge which contains approximately 100 grams of silicagel granules. They can be replaced or regenerated (2 hours in 120C/250F owen will work) and after that your dryer will work as new.
When I opened my -04 compressor unit, the dryer cartridge was soaking wet and there were water drops also in dryer chamber and solenoid (purge) valve. That explained too why I heard tiny sound of splashing water when I shook old removed air springs...
As said, compressor unit is pretty simple piece of device and it's also simple to maintain. Another things to check out regularly are the external intake filter and the hose between filter and compressor. For some reason that hose tends to break down and after that intake air with dust and extra moisture will definitely kill your compressor if not fixed as soon as possible.
Extended life to compressor can also be given by replacing a new piston ring. Manufacturers doesn't have piston ring as spare part, they just want to sell $400 compressor, but there's a guy (Bagpipingandy) who makes them.
After detaching compressor head unit from motor unit, the dryer cartridge can be removed by loosing two bolts. A good video how to dismantle compressor, that's the same guy who makes the spare piston rings too:
Pull off plastic washer from the center tube then lift away metal plate and felt. There is a full cup of silicagel dryer granules.
Internal parts of the solenoid purge valve were wet too. If this valve doesn't work correctly, your air suspension will certainly have problems.
Dryer granules were really soaking wet, the unit was working more like an air humidifier...
