W116, Body and Interior Specific Aid

The plate that holds the tail light bulb sockets has one empty hole which lines up with a red lens cover on the tail light lens. I want to add a brake light socket and bulb in that opening to increase brake visability, which is not the brightest on the older MB. But, I read somewhere that if you do not use the proper brakelight bulbs, it will mess up the cruise control, and if I add two bulbs, will it mess it up.

The radio in my 84' 300d is a Becker Grand Prix Electronic and when I start the vehicle the radio comes on, then cut in and out every 2 seconds consistently. Now if I turn the radio power button off, then turn it back on a couple seconds later it works fine. I want to stay original, any advise? Thanks.

I have been having intermittent hard starting with the engine warmed up. The problem only happens after the engine has warmed up to 80-90 C. The car has new glow plugs decent compression (300+ average)and starts right away when it's cold (below freezing).
The car always starts eventually but I have to crank for awhile 10-30 seconds. Same problem when running on diesel or veg and with oil just changed or ready to be changed. I don't think that I'm getting air in the lines and again it's intermittent so sometimes it starts right up when warm?