I prolly couldn't afford a year, but maybe at least 3 months.
Let's post the #s a few months before the 88 was implemented and then post the #s a few months after the 88 was implemented. In either case, I'm sure the average of the #s were going down. It would probably be too difficult to point it right at 88mms. But I could guarantee that the 88 had no effect on increasing #s, nor would anyone quit because they couldn't use it anymore. In any effect, it does not increase the #s and is mostly a griefing tool for lazy game play.
That's not going to provide the data you're looking for because you can't tell what kind of manned gun they were in. You also can't tell from that data why the player left the game, so there is no way for you to determine that the drop in numbers during those periods were a direct result of manned 8mm guns. The only one that can definitively state the cause of people leaving the game during that period is HiTech. I'm willing to venture that the manned 88mm gun is probably the least reason why someone has left the game, I'm willing to go further that it's probably less than 1%.