I've heard of grasping at straws, now grasping at o-rings!   If that
fixes your leak it would be the first time it's ever happened, IMHO.

I'm on my third core.  They are under-built for the life they lead,
which is usually being left open with coolant flowing 100% of the time.
The constant heating and cooling leads to failure after a few years.
Closing the valve in summer might gain you a bit longer life on the new
one.
--
Stuart MacMillan
Seattle

'84 Vanagon Westfalia w/2.1
'65 MGB (Daily driver since 1969)
'74 MGB GT (Restoring sloooowly)

Assisting on Restoration (and spending OPM):
'72 MGB GT (Daughter's)
'64 MGB (Son's)

Stripped and gone but their parts live on:
'68 MGB, '73 MGB, '67 MGB GT