It depends on which projection set and where it is leaking.
Thomson had a leak fix seal for the expansion chamber for some tubes,
but not the crt face seal.

RCA does sell some of the coolant tank seals and o-rings. Just not all
of
them. Reference RCA/Thompson service bulletin TV94005 about the subject
of Spots on the CRT. Instructions are to remove the primary lens and
use their special design eyedropper to remove contaminate then reseal
unit.
They even give part numbers for the o-ring and primary lens pieces if
lost,
broken or misplaced.
o-ring seal Part number 212073
c-lens 212071
clamp ring 212074
eyedropper 212076

These are meant for the PTK169 chassis and there is other info for
other
models to include the expansion chamber gasket/seal as well.

Coolant will damage the circuit board and components.

Order the parts from any Thomson parts supplier.