Ok, there is no white sludge around the filler cap, and hasn't been at all since i bought the car and the whole time ive noticed the coolant going down.

Although the oil was clearly new.

And i can see evidence of water leaking where you asked me to look. Hopefully this was it but one thing that concerns is would this not have become apparent when i had it pressurised?

Hopefully its just a case of running for the year then selling as i cant afford the insurance for an mk1 RS quite yet (im 20)