not to be the bearer of bad news but your brake calipers are either shot or are going to be shot in short time. The only grease recommended for the brake calipers sliders is silicone grease, using petroleum grease in that spot will literally rot the rubber dampers and boots and allow water to get in, brakes get very hot and the thermal cycling does tend to suck in moisture.
silicone grease is a non melt and non drip water proof lubricant for slow moving parts, It also does not attack rubber.
generic DOT4 or even DOT3 brake fluid flushing is recommended every year to keep the system nice clean and best performing.
The speakers on MB are paper cone, whilst paper give excellent audio performance, their life is next to terrible. I would advise that if you are changing them then please study the system first, the speakers on this car are 2ohm impedance and their wiring is quite a pain to get to. In order to wire a new system I recommend to completely strip the interior and lay down new wiring from scratch. The factory one is part of the body wiring.
Too bad your car didnt have coolant in it from the start, buy a gallon or so of concentrate and mix up a fresh batch at 50% strength, drain out everything (its slow to drain) and fill it up with fresh. If the system is heavily packed with sediment and rust then a citric acid flush would be in order too. If your system was run with dirty liquid then carefully check the water pump pulley and for noise from the pump. It is known to blow out from particles in the coolant.
Also check the front wheel bearings for dark grease, if you do find that the grease is blackened and spent out - and you dont hear any noise yet, refresh the grease immediately. Any good quality GC-LB grease will work. If you dont pay attention to it, you will be buying hubs and spindles.