Any metal plug, bolt, or stud will be safe to use as long as the thread is correct. Using the old nylon washer should be OK as long as it hasn't been crushed from over-tightening. If it leaks, replace it. Teflon tape isn't necessary. Don't over-tighten it, the block is relatively soft aluminum.
"Teflon tape isn't necessary". True, if a dowty or nylon seal is present. But teflon tape MIGHT be all that is needed with a correctly sized bolt/plug and no such seal.
Teflon tape is not suitable for parallel threads. Its purpose is as a lubricant to allow tighter fitting in tapered thread situations. Not as a gap filler. It can sometimes make a satisfactory seal on parallel threads as a stopgap but it is unreliable and the joint needs to be super tight. Super tighten an aluminium thread and you will strip it.
Thats one opinion. It's purpose is certainly one thing, what will work is another.
It's not opinion, it's fact. Try looking it up or asking a plumber. Don't you get tired of critiquing almost every piece of advice that I offer. I don't know what your problem is but if you bothered to fact check before making your statements you might actually learn something.
Nah, I don't get tired of "critiquing almost every piece of advice" you offer at all, because you quite often state opinion as fact. Note that you originally said "teflon tape isn't necessary" not that "teflon tape will not work". After I noted that teflon tape MIGHT work, you get your panties in a wad and then start saying it won't work and look it up and ask a plumber. Here is an actual "fact" for you. When my Yong Heng guage failed, I ordered a replacement and used a short hex head plug to seal the opening. A bolt and nylon washer OR a Dowty under a bolt would have been better but all I had on hand that would fit was a plug. No Dowty seal. No "nylon washer". Just a plug that would not seal the port when fully tightened by itself. Removed the plug, wrapped with teflon tape and tightened. Shazam!!! NO LEAK. It sealed fully and was used until the replacement gauge arrived. Sealed. Fully. Seems to fly directly in the face of your "fact", which obviously isn't such. I'm not saying it was ideal and I wouldn't necessarily use it long term. But it worked perfectly well for either 5 or 6 tank top offs until the replacement gauge arrived. Fact. Not opinion on what won't work. If the replacement gauge fails, I will use a headed bolt and a dowty. But I know from experience I could use the plug and teflon tape. For how long? THAT wasn't the question or implication. But it worked. So, FACT.
