Well I'm starting a Maths degree at Warwick in a couple of weeks, but I did do German A level, and I plan on taking some German modules alongside the Maths. I averaged 90% at AS and got a good A in my speaking, then got a D in the final exam (80/140) moving my overall grade to a B... Anyway, I can try and offer you advice about how not to approach the final exam if you want? :P
I haven't read/spoken/written/listened to any German since the exam... My grammar will still be good though, it's always been one of my strengths. What let me down was content in the writing section (I got 10/25 which then limited all my language marks to 2/5 leaving me with a total of 16/40). I completely choked, ended up writing under the 250 words required, I spent ages on picking the question and making up my mind about what to say. More preparation would have sorted that out I guess. Also AQA and their ridiculous grade boundaries, they were as bad as the year before but the paper was WAY harder. Yeah so just do loads of practice essays, that'll help out there.
Seriously though, my grammar is pretty good so feel free to PM me if you want help with that. Also if you want me to look at any translations, just send them my way and I can offer my thoughts, it'd be my pleasure to help out.