***Shift Problems(Help ME Please)****87 lt250r

[Bobbyday]

I have a 87 lt250r I just bought like a week ago. I have rode it a couple times and everything worked fine. So I figured before I really took it out for a good long ride, i would give it a tune up. I really thought it would be a good idea. Now I'm really wishing I didn't. So I fired it up drove it about a 1/4 mile going threw all the gears. I then parked it and drained the oil, changed the plug, bleed all the brake lines, changed the pads and changed the wheel bearing. Just the routine stuff that i would do every couple month anyways. So when I put back the gear oil I used 1 quart Amsol 80/90 gear oil. I then decided to take it for a ride. To my surprise it will now only shift into 1st gear and neutral. Seriously what did I do wrong. This definitely is not my first rodeo. Did I use the wrong oil? I know the lt's have a wet clutch set up and I was told by my buddy and my local atv shop to use this gear oil. Please somebody throw me a bone. What should I do? Any ideas will greatly appreciated. If I did use the wrong kinda oil, what can I do to get this back to normal. Please please help people.

[wobamf]

You may have to end up splitting the case unfortunately, could be the shift drum I know i lost neutral with no warning at all and thought maybe it was a shifter fork but ended up being the shift drum itself when we split the case, it was just worn out.