Ultimaker BowdenFeeder Repair Kit

You have an Ultimaker and your bowden cable popped out of the material feed mechanism?
Here is the solution:

This clamp goes on top of the material-feed-mechanism (MFM)
Two holes must be drilled to fix it in place.

FEATURES:

• It can be mounted preventatively
  so that your wood clamp teeth don't break in the first place.
• It has round edges, so you dont hurt yorself.
• It has Internal structure and is printable in reasonable time.
• It makes it harder to move the gear by hand and to get your fingers between the gears.
• IMO It looks good.

The more elaborated background story:
I destroyed mine by printing black PLA (IMO more diffecult than transparent white or magenta). The extruder-motor lost some steps here and there for a loong time (no filament scraping! the gear really jumped back). When it suddenly got worse I helped the gear with my hand a bit. But that was too much force then :S . I recognized the damage not before the extruder-motor started to pull on the electrical cables. That was a close call!

edit:
Roman Jurt made an alternative version http://www.thingiverse.com/thing:40544