Hi Gyro.
If you have given the dive unit a slight positive pressure with your bike pump and found no visible leaks around the unit, the only other way you can get any water in there will be a slight 'nick' in the silicone ballast tank feed pipe. This can occurr when the pipe is initially pushed onto the brass tank fitting, the tube can be damaged right next to the edge of the pipe so it's worth checking this. if this is found to be the case, simply chop the tube at this point and carefully re-fit it.
Because the pump line is a high pressure feed, it exceedes the light pressure you have in the dive unit compartments and therefore will deposit water there when the pump is run.
Regards.
Chris