VT & VX is a DASH out job !
The Common cause of the heater core leaking, is cooling system corroded,
and when you do a good flush of the system, the gunk in the heater core is flushed out, and the cooling system works more efficiently and can build up pressure, and will leak at its next weakest point,
or some people twist the hoses off the heater core under the bonnet, to flush the heater core out, and that can damaged the pipe solder joints on the Core
I am still loosing coolant, and its not dripping it, so its consuming it, so I am now thinking its the LIM Gaskets,
I figure, If I am going that far to do those, I am going to do Head Gaskets.
I replaced the Gasket between Supercharger & LIM when I replaced the Bearings, and serviced the Supercharger, a little while back as the SC snout bearing was a bit noisy, so I removed that and pull it down and servicing that.
That's when I had a few more leaks at the next weakest point, one being the Heater Tap, it become brittle over the years, and was leaking on one of the outlets,
I then replaced the Heater Tap, and ALL the hoses [Radiator & Heater]
I removed the old Heater Hoses at the Heater Core by slicing them, and then splitting them open to remove them,
then sliding the new ones on with Gasket Cement,
Done that a few times with our VT & VX some time ago, and more recently with our current VY.