The remote key has a 2 coin batteries fitted. These may have gone flat. Point the keyfob at the car and watching the key press the unlock button. On the key fob there should be a small LED light which blinks. If not, the batteries need replacing. Try this YouTube video. I think they are CR2025 type batteries.
Its possible the glow plugs when its warm the diesel is warm and starts more easily when its cold the diesle needs warming more so the glow plugs work harder in the winter only way i know how to test them is to take 1 out at a time turn the pre ignition on so the glow plug light comes on and the plug should glow red if not buy the 4 and replace the lot you could also check the wireing going to the plugs hope this helps ivan
I hope I'm wrong, but sounds like a wiring harness malfunction possibility. Back in the late 70's, I had a '67 VW van. At night, when I'd turn off the ignition the engine would turn off, as it should IF I TURNED OFF THE LIGHTS, BUT IF i TURNED THE LIGHTS BACK ON AS THE ENGINE WAS SHUTTING DOWN, THE ENGINE WOULD RESUME RUNNING.
Usually if you disconect the battery leave for few minuets and then reconect it it usually spits the cd out as the unit resets itself saves a few 100$ hope yhis works if notbthe mechanisem in the unit has gone you will have to strip the cd player down to get your cd back
For straight up replacments either ebay or a scrap dealer but most head units will fit unless its a double din unit you can get them fitted from new and fitting will cost around the 30 pound mark hopevthis gelps ivan
Its possible that its the cluster its self if possible depending on harness ect can you swop the clusters around left to right ect just to see if the lights work with the cluster swoped round the old ones had just 1 plastic tab thing that keeped them in the light part and the cluster bulbs ect where a seperat part if it was fuses ect all the lights would go off not just one side check earths ect they may be behind the cladding bits at either side of the boot make sure there ok hope this helps ivan
The voltage regulator in the alternator has probably failed. The AH rating of the battery has nothing to do with it. This is why I would never own a MB, too many gadgets that cost a fortune to fix when they fail.