Our house dates back to 1955 and features several fancy items not found in contemporary dwellings. Take, for example, the Thermador in-wall heater in the front bathroom:
It has a finger-friendly design apparently intended to admit a small finger through the grille, where it can easily contact the resistance heating coil, so while we were moving in I snapped a GFI circuit breaker into that slot in the breaker panel. We advised our (very young) Larval Engineer of the hazard and had no further problem; as far as I know, that breaker never tripped and no fingers were damaged.
Back then, while adding that breaker and cleaning the first half-century of fuzz out of the thing, I evidently blobbed silicone rubber on the screw terminals of the switch:
They don’t make switches like that any more.
For reasons not relevant here, we’ll be using it for the first time since we moved in, so I spent a while cleaning / blowing / brushing another two decades of fuzz out of it.
Minus the fuzz, the heater no longer smells like a house on fire:
If that doesn’t warm your buns, nothing will!
The Smell of Molten Projects in the Morning 
Those switch contacts could benefit from gentle treatment with a diamond fingernail file or a folded piece of emery cloth.
That thing stays in place until smoke pours outta the vents! [grin]
My grandparent’s homes were full of these and all of them still worked. Additionally one home had a “portable” and outlets all over the house that were 220. I don’t recall what we did with it when they passed away but I should have kept it as a huge load bank but it was quite heavy.
If ours is any indication, those heaters had a very low duty cycle and, being built with Real Metal, should last forever.
I’m sure the “portable” version weighed more than a small child and, despite having handles, was portable in name only.