Um, copper is an element. It can't have any lead by definition.

Brass may have very low amounts of lead, even under current regulations. However, for many years now, a brass or copper boiler has to have a non-reactive coating like electro-plated tin.

Stainless steel - the 304 variant typically found in many home machines - has its own issues with corrosion from chlorides in water, low pH water, and also galvanic corrosion. Corrosion/pitting of 304 will leach heavy metals into your coffee. Lead may be the most commonly-known heavy metal, but chromium isn't exactly a health food . Upscale/commercial machines have pretty much switched to, or have always used, 316 stainless, which is much more resistant to chloride corrosion than 304. 304 is much more common in primarily non-commercial espresso machines because a 304 boiler is less expensive than a copper or brass boiler. As such, non-commercial espresso machines switched from copper/brass boilers to 304 to reduce costs; ECM's lower-tier line, Profitec, was a big early proponent of using less-expensive 304. In addition, some say stainless is inferior to copper/brass due to wetter steam (unless steps are taken) due to lower thermal conductivity of stainless steel. https://coffeetechniciansguild.org/blog ... ded-coffee

In other words, the material doesn't matter as long as the machine is properly maintained, including good water. Even a vintage machine with uncoated leaded brass all over the place will not leach appreciable lead into the brew water if the machine is properly maintained/used. However, those machines rely on proper maintenance and use to control lead leaching, which is not what current regulations are willing to assume.