VLSD question.

[KAs14slider]

Hi guys, I have a s13 vlsd in my s14 and it just does such a poor job of locking most of the time. I can't even do a 180 from a dead stop or do donuts because it usually does a one wheel peel and locks only when it feels like it. I plan on getting a nice 1.5 or 2 way next summer but for now I can't afford one. Now, I just realized that the oil in it has never been changed. I heard somewhere that you should just put in the thickest stuff you can find and it will help those the crappy vlsd's lock better. So my question is what fluid should I put in the diff? Should it be synthetic? Also, if it matters, I live in PA and right now it is crappy winter weather. Is it better to run different weight fluid in summer and winter? And when you change the fluid, do you just wait for it to drain and then add new fluid until it starts dripping out of fill plug?