A little late to the punch here, but still...
WD40... ugh... that will just lead to nasty funky gunky mess of goo, hair and dirt all over your cart port and cartridges.
First try Alcohol... you can soak a junk t-shirt with it, then stretch it tight over a butter knife and shove in and out(no side to side) and be careful not to snag any of the pins so you don't pull them out.
Then there's also Deoxit.. a bit more expensive But from my experience it works really well and I generally go straight for it instead of bothering with alcohol if I have some handy.
Then as previously suggested:
After that comes bending pins with something like a dentist pick.
And then just getting a replacement cart port... which is what I ended up doing with my NES after the alcohol failed.. back when I didn't even know deoxit existed.