Tried to PM you your box is full. I sent my cell phone number to you call me, I'll help you out.
1. Box w/Heat Gun or Oven is good, both work. Heat gun by itself not so good.
2. No need to clean off excess sealant, push it back into the grove.
3. If you do remove sealant you may want to get some new sealant to keep light from leaking:
OCI Butyl Rubber Glue - Accessories from The Retrofit Source Inc
4. Box works fine just don't point the heat gun at the light in the box. You do that it will melt and soften up the plastic.
https://www.youtube.com/watch?v=PaXz...ure=plpp_video
No matter what method you use the plastic tabs will be delicate. Just be careful. I put the lens back together and test fit it. Then leaving it together I warm the hole thing up in the box. Then push it all together, I'll do that as many times as I have to. So far i have done 6 sets and I have only had to put 1 set back in the box to re-heat 15 min.
Hope this helps, call me if you want, always here to help, anytime.. Thanks