i was running my s2 on 4500 weight shock oil, tuk it on the track wow really really stiff bouncing every ware, i have upgraded my shocks to s3 hopup shocks there better but the back needs refilling, i wana no a good weight oil to put in there (1/8 scale , 4wd, 21 engine, for racing on a bumby grass track) can some one help please