Due to water and oil getting into the centre tube the bearings and seals are being replaced.

Question is how did the oil/water get in? with only a 'drain' (as described in the parts book) plug at the top of the tube.

To drain any future liquid from the tube. I have now drilled two drain plugs which are protected by being under the front and rear skid plates.

Note: two drain plugs are required as the centre bearing would trap liquid either side of the tube.