My yamaha majesty is blowing from the joint where the back box meets. Ive tryed joint paste bandage liquid metal. My.question is can i use a rubber tube like on a 2 stroke i mean temp wise o only need it to hold till next week till the new 1here. Thankz in advance

The simple answer is "NO" cos it gets hot and all you will do is make a sticky mess, why not try an old tin cut to shape and jammed in the gap till you can replace it, won't look pretty but might just get you through a week.

PS worst case scenario is that if you use rubber tube it will catch fire and burn your bike to the ground ok if you have TPF & T but the insurance company will be snotty about a claim.