manual transmission fluid

I'm looking at changing tranny fluid in my P5 and wondering what GL class I need?I'm looking at Redline MT-90 75W90 and they say GL-4 is popular with Mazda, so I should go with GL-4? thx

Most part places like Advanced Auto and AutoZone and Oreilly's have the correct fluid for it. I personally wouldn't waste the money on Royal Purple...its pricey for what you get. Unless your car is like 350-500whp and you drive it at the track 24/7 Royal Purple is not necessary. I friend of mine does a mixture of 2 quarts synthetic and 1 quart regular, of the same weight. His mechanic recommended that to him and his Mazda3 is 300+hp boosted at 10-15lbs. and his mechanic has been building track cars for years, so I trust his opinion. That's what I'm doing when I finally get my tranny back in and fill it. Good luck!

GL4 because i didnt used some cheap stuff and now my 3rd gear grinds=(