Driveshaft slack/backlash - How much is normal?

[jy116]

Problem: When i step on the gas and let off abruptly consecutively a few times [in gear], i can hear a slight, muffled clicking noise... like play in the driveshaft.

Checking: I jacked up and got under the rear and rotated the driveshaft by hand [with the e-brake off] and theres a little play on the driveshaft b4 the wheels start turning. Maybe like ~5 degrees of rotating b4 the wheel moves.

I looked at the FSM under PD [propeller shaft +diff] and says "runoff should not exceed 6mm". Seems like this refers to the driveshaft longitudinal play [lengthwise], so Im not sure if that slight slack [backlash?] is a real problem or if its normal.

Specific Info:
*I got a used VLSD, supposedly JDM, 6 bolt flanges, been on for ~2k miles, didnt change the oil when I got it cuz my frend put it on b4 I could do it. I know its not too major cuz the viscous diff itself is sealed with its own lubricating silicone crap. Dont thnk the pinion gears would wear after ~30km [in JDM land] and 2k miles...
*I had a auto to 5spd swap done, the driveshaft is half from MT and the other half is from the orig AT driveshaft.
*Car drives fine, just worried now cuz I signed up for drift practice on March 19 [see USA thread, "SCCA Drift Practice"] and dont want to break anything or forfeit my $75 spot!

Some one who drives hard/drifts their s13 wana check this to see if its normal? U can rotate ur tires/change ur diff fluid while ur at it?! ;]