I used to repair Xbox's for a living due to being ill and not allowed out of the house. I repaired every one that had not been previously repaired (over 100) with similar kits but only ever used 'Arctic Silver 5 paste'.
This is by far the best site for instructions.
'''NO''', these kits are not guaranteed to last. Some Xbox's I have repaired lasted over 16 months, others only days if that. If you do decide to try this yourself, invest in a proper 'opening tool' and a decent Screwdriver set with 'Torx Accessories' I use the 'Draper 31 piece precision set' - stock no: 09550 that I bought off 'Amazon' and is great for changing the lasers as well. Infact I use it all around the house, and on my VW Golf.
If your logic board or 'Mother Board' is warped, or you want a 'guaranteed to last a while' solution, you need to have your 'Mother Board' RE-Balled. You could go down the road of a RE-Flow, but it wont last as long. The machine used to complete these repairs costs around £1000.00 Sterling, so the repair costs are around £50.00 + cost of shipping both ways.
I just thought you might like a professionals opinion and not just some youngster that got lucky - I am in my 60's and have been repairing electronics for 30 years.