When a customer asks what kind of oil to use I'm sure not going to give them a bottle of transmission fluid.

It's exposure to the air and the consequent oxidation that's the problem.

Think of it this way; linseed oil is a 'drying' oil, meaning that it oxidises and polymerizes (turns into a varnish) very readily.
This is considered to be a desirable thing, because linseed oil is used as a wood finish.
Linseed oil remains a liquid while it is being shipped and stored in bottles, but when it is spread thinly on wood and exposed to air, it gums up and then hardens.

Oil stored in bottles isn't a good indicator of its resistance to gumming/varnishing, because the bottle contains only a limited amount of oxygen.

ATF contains antioxidant additives to further prevent oxidation even when exposed to air, which is one of the reasons I'm so enthusiastic about it.

Well go for it James. It just seems a bit unprofessional to me.

I never suggested that you should recommend this to customers.
It's different if you're running a business.
I can totally understand why you would not want to recommend a product unless it is specifically made and sold for sewing machines only.

What product do you recommend to your customers?

You are STRONGLY recommending ATF to everyone on QB at least it seems to me - so what difference does it make if they are your customer or a quilt lady/gent?

I now recommend regular everyday sewing machine oil from the most convenient store that has sewing machine stuff. It is easy to find and use. It is hard enough to get people to clean a machine and oil it with out having to worry about what kind of oil to use. Getting out dried up oil is another matter. Some times one thing works some times another depending on what you are trying to remove. Until something better comes along, I will continue to use T-F.

That's part of the reason I like ATF so much; it's even more widely available than sewing machine oil.

I understand where you're coming from though with customers. It's certainly easier to explain that the bottle that says 'Sewing Machine Oil' is what they should buy, rather than explain in depth the virtues of PTFE lubricant.

I expect you'd probably meet with a lot of resistance for suggesting something new and different.

Transmission fluid has been around for a very long time - nothing new or different about it at all. For cleaning about any oil with a solvent will clean dried up oil - it is how much damage it does to the paint. I try to go conservative on that. For oiling a thin oil will work. BTW I did some research a while back with a man who ran an oil lab. You can use your transmission fluid - but I don't know why you think you need to make such a big deal about it.

I didn't make a big deal out of it. Everybody else did.

you believe that?

All I'm qualified to do is be a cheering squad - but Wow! You all are so knowledgeable it is amazing!