That's a good question, and a controversial one, but one that I will dodge somewhat by saying the following. The way we usually work is to reproduce a gasket from a customer supplied sample, blueprint, or template. We do that using material as close to the original as possible, or as specified by the customer. I generally refrain from offering advice on whether or not to use a sealant because there are so many variables that I may or may not know about. What I do advise is for them to follow either the OEM mfg. advice or to follow the advice of fellow enthusiasts, since they are in a far better position than I am to know the situation as far as their particular application.
I will give you an example of what I mean. I have some customers who run old Lister diesel stationary engines. Many of these are copies produced in India, and because of poor surfaces and poor gaskets on the OEM equipment they are prone to head leaks. I know from my customers that they like to spray their gaskets with copper spray, and that seems to improve things for them. We make a silicone coated composite gasket for those models that seems to have stopped the leak problems, and I don't think using a sealant is necessary. I mention this as an example of an instance where a particular 'community' has derived a consensus opinion on the suitability of using a sealant.
Finally, there is one more reason that I generally avoid taking a side on a sealant issue. Having produced a gasket to a customer's spec, if I advise one way or another on sealant use I am just increasing the possibility that any subsequent failure might be blamed on my sealant advice, whether or not that is really the case.
I will give you an example of what I mean. I have some customers who run old Lister diesel stationary engines. Many of these are copies produced in India, and because of poor surfaces and poor gaskets on the OEM equipment they are prone to head leaks. I know from my customers that they like to spray their gaskets with copper spray, and that seems to improve things for them. We make a silicone coated composite gasket for those models that seems to have stopped the leak problems, and I don't think using a sealant is necessary. I mention this as an example of an instance where a particular 'community' has derived a consensus opinion on the suitability of using a sealant.
Finally, there is one more reason that I generally avoid taking a side on a sealant issue. Having produced a gasket to a customer's spec, if I advise one way or another on sealant use I am just increasing the possibility that any subsequent failure might be blamed on my sealant advice, whether or not that is really the case.