The tilt sensor schematic
(http://www.brickshelf.com/gallery/jorgepereira/WeDO/tilt-sensor.png)

Based on Philo photos of the WeDO internals
(http://www.brickshelf.com/cgi-bin/gallery.cgi?f=434406)

R1 = 3k9
R2 = 10k
R3 = 6k8
R4 = 1k2

The value of R1 is critical - this resistor is connected between C1 and Ground (0V) and it is used to identify the tilt sensor - if possible use a 1% tolerance resistor.

The other 3 resistors are not so demanding because the driver of the tilt sensor accepts a range of values for each of the 4 possible states.

More info at http://ofalcao.pt/en/