I just did mine before I put it on the road again in March. I put Castrol Syntec in 75w-90 (Honda calls for 90w, hypoid type, either GL 5 or GL 6).

Some useful information if you are planning to do yours:

You need a 24mm socket for bottom plug(drain), 23 mm spanner for the side plug (refill). Torque both to 33 lb-ft when tightening back up. Fill to the bottom of the side refill plug hole (car level). Takes less than a litre (one jug will do you). Buy a syringe/lubricant plunger to refill, as you need a flexible hose because of the tight fit and you cannot pour using gravity...

 

Thanks for the tips. This was recently discussed in the Car Talk forum http://www.s2000online.com/forums/showthre...p?threadid=7458