tranny goes 'ding"

tranny goes "ding" on my'67 300 440/727 58150 original miles SOMETIMES when I shift into drive or when I shift into reverse. Idle seems low enough(no tach) and yes the brake is always engaged when I shift. And although there's never a "ding",sometimes the 1st to 2nd shift is very obvious and other times its so smooth you cannot even tell it shifted. The fluid is good and red, no burning smell, no dirt,good level but it might be original from 1967!!! There is about a teaspoon-per-week leak where the bell housing meets the engine but I can't tell if its oil or oil and tranny fluid mixed. Any advice would help.
Thanx,
Big300

With the mileage your car has, it is probably a good idea to change the tranny fluid and filter anyway. Most folks leave this maintenence undone until it causes damage. If you leave the old fluid and filter in there until you can tell a change in performance, it has been left in there too long anyway.Every Mopar I ever had was a little noisy shifting into reverse occasionaally. If the U joints are ok, and there doesn't seem to be any excessive slack in the drivetrain anywhere, I wouldn't worry about it.As for the leak, your intake manifold gasket may be seeping some oil.There are little rubber or cork oil seals at the end of the intake pan that get hard with age. This is not too hard to change, just pull the intake,leaving the carb attached to the manifold.This ****** is heavy!, so be prepared when you lift it off.

My 73 Duster made the same engagement noise and was due to slack in the rear end pinion gear (and differential housing was almost dry on grease and sludged). I changed the gears and made some adjustments as well as an obvious fluid change. It solved the problem and is worth a look for your vehicle. Check for slack at the rear end gears.