every so often when slowing down in second gear only, it throws itself into neutral any ideas why.

it a 98 car with ppp and quickshift?

 

I had this problem on my MY95 STI RA and it turned out to be a full gearbox job! Second wasnt oiling properly due to the previous owner in japan kicking the backside out of it in second gear and jumping out of gear soon developes into stuck in second/cant use second.Please get it checked out sooner rather than later! Dip your gearbox or drain your fluid and look for swarf. I hope im wrong but that is how it started for me!!
Good luck
Callum W

 

How much swarf would you expect to see? I've not got this problem, but my gearstick rumbles slightly in 3rd after lift off...I've changed the oil many times - every 10k to 3k during the tek3 retune and bigger turbo - and I've only seen 1 small 'c' shape swarf...and the metal crap collection plug is fairly clean.
The gearbox seems to have stages of being very smooth (feeling from gearstick) and then rumbles...sometimes in other gears then 3rd.

 

Sounds like second is not going in far enough, maybe a bent selector fork, as mentioned can lead to breaking of the fork and leaving you stuck in a gear.