Here's how you do it:
Go to Valley Windworks
1) Slather a tree which is NOT the previous one you slathered, check back in six hours of game play and check if you got a muchlax.
If not go to step 1, if yes go to step 2.
2) Once you have encountered a muchlax capture it, then slather the same tree. Wait 6 hours, if you get munchlax again repeat this step again, otherwise repeat step one.
If you do not go to a different tree after failing to get a muchlax your chances are .01%.
If you go to a different one after failing to get a munchlax your chances are 1%.
If you do get a muchlax, going to a different tree your chances are 1%.
If you do not go to a different tree after getting a muchlax your chances are 91% that you will get munchlax again.
Sorry about you waiting so long, that fat thing is so lazy.