Mate, get the car up at the back end and check the rear arches out for any specs of rust. In the winter, they rust ferociously if there's the tiniest spec of bare metal. Take the rear quarter panels off the inside (next to the rest seats), you will see if they've started by looking down into the cavity. If they're clean, cover the whole inner arch with waxoyl. The lip under the bonnet also 'goes', loads of stone chips get under there and water collects and away it goes. I just spent an age doing mine (they were completely shot), not a nice job.
BTW, I was paying 1,300 on my GSi, with 0 ncb with Tesco insurance (!!!). I got my finger out and found my old certificates and now pay 650 3yrs ncb with Liverpool Victoria.