As Mod BB said we do discourage the average civilian from doing these type of repairs. Those that I've learned are the proper safe way of these repairs that I can do, but there are a lot of precautions that must be adhered to. Even the professionals can make mistakes. It is best when in doubt don't do it and just replace instead.
I have seen mechanics smoking around open flammable liquids. This something I highly discourage which is why if a smokers approaches my shop I stop them until they put their ciggies out as there is a high chance that I am working with flammable fumes within my shop even though it's a well ventilated area.
