NO NO NO additives in the coolant. Only making a headache for yourself. Also, while you're at NAPA pick up Zerex G05 coolant. This is the coolant that these cars agree with and it is made by the same company who makes Benz coolant for half the price (Valvoline). I would just get the buttons from the junkyard, I doubt they would charge you anything except a $1,00 at max. Yes, I would look into adjusting the transmission also and checking the vacuum lines. Crucial in transmission shifting. This is all on the forum by the way.