I agree, use the atf. Theres a lot of original t5's running around with 150k with nothing but atf.
while i can't verify, i've heard the gm sincro mesh can eat sincro's in a t5. no reason to get fancy with synthetics or sincromesh, just run the damn atf.
Hmm... My brother and I both have been using the blended synchromesh for about a year and we both race. I havn't experienced any adverse effects from using it. Shifts easier under power. My tranny has 150k on it and my bro's is a T-5Z and has only used syncho in it.
I didn't mean to say that Synchromesh will break your T-5, I just meant that it's a waste of money when you should really be putting ATF in it......I assume Synchromesh costs more money.