Search for the thread titled below..... it might be of use to you as this was a 2004 S-Line to S3 conversion. If you go for an S3 conversion from a twin front grill, you'll need the correct bumper and match that with a newer single grill bonnet....
--- Single Grill Conversion Done....V6 S3...
Try and check the inner cv joints for any play as we had the same problems with Sarah's A3 3.2, you can easily check them by holding the drive shaft and physically lifting it up/ down and sideways etc for any small signs of play.
Yes, I had the LCR splitter fitted and for only £20 ish, it was worth it, just needs trimming and the ends when fitting.
took it off when we shipped the car to Oz and not got round to refitting it yet.
To answer your bhp question, have a look for the sticker in the boot / spare tyre area, there should be one in your service log book too near the front page. There will be a KW power rating for the engine, simply multiply this figure by 1.341 to give your bhp.
When you say you tried another control module, I take it you took your own out of the black plastic box, in the footwell. Was it dry? Were the connectors corroded at all? I had water in mine and had to clean up the pins/ connectors.
IIRC, with mine, headlights on of course, It's every second or third squirt, as I hold the stalk for a good squirt. You can easily see it working as you drive along at night as you can see the spray from the lights over the bonnet.