with the heat and vibration, do not think it will last long. only two suggestions other than new:
1. stainless fastener which will require drilling a hole
2. spot weld which will possibly cause minimal heat damage, cover with high temp paint
Its very hard to fix any cracked heat sheild the best thing to do in get a new or used one. JB weld is great stuff it may do the job for a while unless your a good welder or know one replace it for a good peace of mind.