That joint looks to be a Raleigh Technium. Great riding bikes so far as I am to understand. The lug construction however, used an epoxy that was applied between a hot lug & a cold aluminum tube and the 2 were then swaged together in an interference fit. In theory there should be nothing wrong with this arrangement.
But as all bonded things have the potential to become dis-bonded, if water intruded, the aluminum would be the sacrificial anode.
I'm not sure what I'd do in this case. I don't like any of the scenarios.
Is there a way available to test the white residue to establish what it actually is? Wax would be the best possible result. Aluminum-oxide would mean retiring the bike.
EDIT: Is this relevant?
https://www.cpsc.gov/Recalls/1996/CP...e-Frame-Recall