Just an old fashioned flushing with water until clear and drive until it hit normal operating temps. Then cool down and do it again.
Sounds like a plan.
My opinion (only), I don't see that coolant flush solvent will damage to seals or to gaskets.
Now with that said,
if cooling system has a lot of deposits in the system,
and if any previous leaking gaskets might be plugged from settlement or debris.
Cleaning out all of that “stuff”
will re-open those leaks.
Example: I have replaced a few hundred freeze plugs over the years.
A lot of them rust from inside out. On the ones that have rusted from inside out, they are generally the ones towards the rear of engine, and generally have at least an inch of “stuff” (or crud) right behind the freeze plugs. If a person was flush the system out, then all of that “stuff” (or crud) would have been flushed out, leaving the mostly plugged rust holes already present (but barely leaking now) now opened up.
Note: those cars take a lot of water and a lot digging with a coat hanger, to get all of that mud out.
On a different topic. I have listened in on a lot of lectures as to why to change coolant/antifreeze every two years (in reference to the “green” coolant, not the new fangled stuff in use today).
Coolant/antifreeze has three purposes in life: a lower point of freezing, a higher point of boiling and rust/corrosion prevention.
Glycol doesn't go bad, per se. The rust and corrosion prohibiters only last about two years – which is the reason to change it.
I do know you can tell, by working on any older car, if coolant has been changed every couple of years or so – vs. not.
Personally, I think that lack of rust and corrosion prohibiters is the main reason for most heater core failures (note: no proof of this – just my theory only).
In my opinion, I don't see any problem with using flush solvent – for I would rather find those leaks now, than later.
Also ANY cleaning is far better than no cleaning!
Also note: either use 50/50 pre-mix OR 100% Glycol coolant mixed 50/50 with DISTILLED (only) water. Never use tap water – for it will promotes rust and corrosion.
BudW