If its making you tingle, toss it! Its leaking current, maybe not enough to trip a gfi, but if it deteriorates further its dangerous!
It may be that the plastic barrel is a better insulator than the glass tank. And if its on concrete and you are standing on concrete when when you feel the tingling, guess where the ground path is? Yes its YOU!
The glass tank may have a slightly better ground path, or you are insulated better(standing on carpet or a wood floor)enough that you feel nothing.
The fact that you feel tingling means its leaking, so rid yourself of a potentially dangerous heater!
I work with electricity on a daily basis, and more people get hurt with 120v items than anything else, dont end up being a statistic!