replacing those bulbs
I don't think bulbs "wear out" as parts do that are subject to friction.
Annoyed by the somewhat high prices of fuses and bulbs (and even more by the nasty habit of the chain stores bubble-packing these things two or three to a card) I began harvesting such things from u-pick junkyards, where some believe that small stuff that will fit in your pockets is, well "free". This is the attitude of the tattoed ex-cons that clerk at the U-Picks I frequent. They don't charge for small stuff, because they assume people will just stuff it in their pockets, which I thing most u-pickers do. When I put bulbs and fuses on the counters, they snort in a scoffing way, as they might at an altarboy who returns Fatjher Flannigan's unused mustard packets to the Ho Jo.
Fuses that are corroded and bulbs that have that black haze on them I don't use, but I have found that a junkyard bulb often needs replacing no more often than one bought brand new.
Many Benz bulbs are quite hard to find as well, and if one can find a nr. 2207 DRG Fischer 12v/4/mHC bulb such as fits in the automatic transmission shifter of a 123-300D, at the U-Pick, one should take it, because that bulb is only available in the most esoteric of specialized lightbulb shops. It is ecologically sound to do so, as a six-mile trip to purchase a $1.50 bulb uses almost as much in fuel as it costs.
I suspect that what makes a bulb fail is not that excessive use has taken away all its electrons, but that it was manufactured with a teensy amount of air in it, and that air corroded the filament. If the bulbmaking apparatus pulled an absolute vacuum, then I assume that the bulb would last eternally. Many of the bulbs in my 1977 Celica lasted through the 160,000 miles and 26 years of its life. A bulbmaking machine that made perfect bulbs would, I fear, go unrecognized.
It is a good idea to get some dielectric or "bulb" grease to put on your bulbs, as this keeps them from soldering themselves inside a socket and requiring a surgical (or needle-nose) extraction.
So I would say that bulbs are like the lottery: someone has to win the lottery, but probably not you and probably not today. At some time your left turn signal will go pffft but probably not that bulb and probably not today. If you have a supply of cheapo bulbs on that rainy Sunday in Yeehaw Junction, it will bring a warm feeling to you: trust me.
By the way, access to the auto transmission light is easy: just remove the ashtray, remove the two screws and the bracket under it and lift up on the wood trim: removal of the entire fool console is not necessary, as the Haynes DIY seems to suggest.
Semibodacious Transmogrifications a Specialty
1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)
"Time flies like and arrow, yet fruit flies like a banana"