Oil change in my 5-speed manual

[mystar]

I just bought a one-owner '93 C1500 with a 350 and 5-speed transmission - RPO code 'MM5'. It has 125K miles on it. The original owner said he had never changed the transmission oil at the advice of his local dealer. Sounded strange to me, especially since he had detailed maintenance records on everything else. I am not having trouble with it (although the throw-out bearing seems to be making a little noise), but, I have 2 questions:

1. Should I change the oil now?

2. If so, what oil do I use??

Thanks,

Mike in TX