Well, a frontal attack with stuart is not the most effective and chasing a sniper can lead to losing the tank to a teller or faust/ pak combo. Snipers usually operate around a pack, teller or gren to be safe.
The most successful option takes a bit to setup but basically requires you to push on one front with all your rifles spread out so you don't get pinned and basically swarm towards the sniper. Most times when faced with such a dangerous threat the sniper will retreat. The stuart will be then come from another direction and basically meet the sniper in the base. If he retreats everything then hold off and try again.
The other option is try to position a bar squad (Lt) or para with smg in the retreat path when you push towards the sniper with the rest of your rifles. Can be tricky and often futile but your best chance to kill it is on retreat, in my experience.
Sure this one way to do it, but will not work with someone that can use a sniper by it's full potential.
Before the sniper was buffed I got some insane games with atleast 80 kills. But I surely had to babysit it. After the buff I also use them but now I give my other troops some more attention. Also I don't retreat it right away, but I will just hold fire, move into cover and retreat to the base in cover. Not gonna lose my sniper to a m20 or stuart.
But the biggest part of me when losing my sniper is the somewhat lesser attention thst I give it. Just get the focus of the sniperuser to something other important and then strike! Probably more effective.