Erratic tach - usually poor connection at the tach amplifier under the hood.
Either the female pins on the plug (aka diagnostic port) have spread open too much or there is a cold solder break in the amplifier itself.
The plug can be disassembled and the female pins can be lightly closed.
The circuit board can be re-soldered - but you have to chip away the silicone anti-vibration filler first.
I disassembled my plug and tach amplifier on my 83 300SD and replaced the defective tach amplifier with a good used unit from the local Pick-n-Pull.
Dash lights - check your fuses. Spinning them in place or removing and reinserting can often re-establish a balky circuit.
2). Paint - shoot an email to the
classic center with your VIN and request a copy of your build sheet.
They are an invaluable resource and may be able to supply the touch up paint (as well as other parts you made need going forward).
3). Windows weak - regulator arms tend to bend due over time (especially driver's window) due to lack of an auto stop switch when window is closed.
Also may need to lubricate window guides and replace any worn pieces.
4). Door locks - vacuum operated. Master switch is in the driver's door.
Driver's door must be closed - central locking system operated by key in door or by door lock button inside the car.
5) Radio and speakers - Blaupunkt is an original supplier. AKAIK build sheet should list the unit the car came with originally.
6) Rust points - Under battery tray, lower front and rear windshields, rocker panels, wheel arches, hood hinge pockets, lower door seams.