I'm going to s*it on both sides of the fence; I've done it both ways in many situations. Brass on brass and about any other type including a steel motorcycle tank, the brass (or, in the case of aluminum, the Al threads) will deform just enough to seal if I was too cheap to buy tape or dope. With the addition of sealant, its like very inexpensive assurance.
This is a NOS petcock going into a original factory 69 radiator. Maybe I should ask how did the factory do it back then. I do have both pipe dope and teflon tape in my toolbox, so no big deal. I just like keeping things as original as possible. Many thanks.
