If all you want to do is upgrade the slipper clutch you have a few choices.

1) You can superglue the clutch in place

2) Replace the clutch with a solid gear (Blue)

WARNING - While both option should eliminate any slippage, they will also defeat the safety feature of the clutch.

Tamiya sells a series of gear boxes for various projects. What you need are the blue gears to replace the clutch.

Gluing or eplacing the clutch with a solid gear can also be used for a slipping turret motor, with similar warnings.

Good luck