Use a general rule, try not to use anything that claims to be special (such as '3-in-1'). You just want very basic, Silicone-based gun oil as a lot of these off-the-shelf things have various 'go-faster' additives that just eat away at your plastic over time, and generally screw things up.
Basically what I'm saying is that if you're not totally sure what to get, then stick to a known brand like Abbey; it's £7 a tin, and will last you for a good couple of years.