1964 Valiant Slant 6 to 318 Conversion ?

The leaks could just be a bad pan gasket, or front seal. Where are the leaks: coming out of the bell is a front sealleak, time to remove the trans. Pan leaks are just that: pan gasket. The push button shifter mechanism is usually not the fault as its just a push/pull affair. The 'rooster comb' detent spring is the thing that gets the trans in gear, all the push button has to do is get it close and the ball detent will lock it in. There is an adjuster wheel on the cable where it enters the transmission. it can be turned to adjust the cable like a bike brake cable ferule. Here is a read about it, kinda lengthy but may save your *** when it comes to paying for someone trans shop to ask their grandpa to adjust it for you.

• Update March 2014: Paul L. notes: “My 2 cents: I have used the Factory Service Manual method, test light method, Ohm meter method, and eyeball method. What I found was that there is a little inaccuracy in the shift cable mechanism. If you line up the neutral detent with the neutral safety switch by eye it will be close. However you need to use the push buttons to shift the mechanism a few times to see where things will 'land'. Most of the time it will be off slightly. You can then use the wheel to fine tune things. An analog type Ohm meter is then helpful because it will show if you are slightly off by showing varying levels of resistance as you adjust it in and out. The test light will work this way as well with the light getting brighter or dimmer as you home in on the sweet spot and the neutral safety switch makes good contact.”

(Hook up multimeter to back up switch and shift to R, check for continuity of meter and adjust to get highest reading /lowest OHM or test light brightness)

• Steve C. replies: “You’re absolutely right, Paul. Depending on the condition (wear, bends/kinks, etc) of your shift cable, there is lost motion (hysteresis) when changing directions.
  
  ...
• 
  
• 
  This is an extreme example, but exactly what happens with any push-pull type of cable application. This is the reason for the 'rooster comb' on the manual valve lever - basically we get it close with the shifter and cable, and the spring and ball force the rooster comb to precisely the same place every time. Unless of course, your cable is sticky, corroded, kinked, etc. and won’t allow the manual valve lever to move that extra small amount.
  
  Having fine threads and adjustment holes at 60 degree increments allows length adjustments of as little as .007" per hole, so finding that perfect spot is ensured, again, depending on the condition of your cable. And again, as long as there is not significant friction in the cable, close enough is usually close enough.
  
  So if you’re having a problem getting a 1962-1965 shifter adjusted properly, first check the entire system for lost motion. The shifters (pushbutton, console and column) are very robust and seldom the cause of problems (despite what you’ll read other places), but any attaching points of either the inner member or outer housing can cause issues.
  
  Starting at the shifter end, check the fit of the eyelet on the shifter pin (not usually worn but sometimes the wrong cable is used), the fit of the bayonet 'pointy end' into the adapter, and the fit of the adapter into the manual valve detent lever (often incorrect if parts have been swapped or modified). Also ensure that the eyelet and bayonet are securely crimped to the wire. Check the housing mount where the shifter (or bracket in the case of pushbuttons) is crimped to ensure the connection is tight and there is no movement. For pushbuttons, make sure the bracket is tightly screwed to the pushbutton unit. You can use a thin nut inside the pushbutton housing in the event of stripped holes. Then check the integrity of the crimps at the upper ferrule and the adjuster to be sure the housing isn’t sliding in and out as the cable is moved. Finally, check the threaded adjusting wheel to ensure there is no significant motion at the threads (there will be a few thousandths) and that the wheel is securely attached to the transmission case.
  
  Last, if your transmission has been rebuilt or repaired, be sure the manual valve detent lever spring is of correct size. Very few transmission shops have the correct spring, and since the original spring is very light (we are, after all, shifting with plastic pushbuttons), technicians often replace the spring with a heavier one, as it’s obviously 'better'. Too heavy or long of a spring requires additional force to move the detent lever, resulting in bracket deflection, loosening of crimps, or accelerated cable wear. In extreme cases the inner member will kink. It should take very little pressure to move the manual valve lever, unlike the 1966-later models.
  
  The bottom line is that the pushbutton shift system (as well as the console/column variants) is very robust and dependable. Stories of adjustment horrors are always the result of worn, damaged, or incorrect parts. Like the ball and trunnion, pushbutton vintage shifters get a bad rap because they are different, and many would rather swap them out than learn about them.

Mopar Push-button transmission tech tips