Penny wise and pound foolish. The primary method of demise for these vehicles is, almost certainly, rapid and unexpected loss of coolant leading to overheating and head damage. You have a nice turbo w/47k orig miles man! The radiator will cost ya >200$ and take less than 2 hours to replace...

The fibered stuff will work (Bar'sLeak) but recognize that it is (1) short term) and (2) will risk plugging other stuff up like your heater core. Unless you are broke or totally occupied, best advice is to spring for a new radiator (Nissens aluminum/plastic unit from FCPGroton) and two new hoses. And if you are on your original heater water valve and heater hoses, you are long overdue for a massive failure there.
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See the 700/900 FAQ at the drop-down menu above right.

I would suggest that you take the rad out and go to a repair shop and just do it, magic fixit stuff isnt worth the effort of putting it in the system,
Good luck

I'm sure that the AC/Delco cooling system leak-stop stuff I got at a GM dealer was not made by GM, but presumably it passed their tests by not plugging up heater cores and so on, so I'd suggest it in preference to something off the auto parts store shelf.
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Bob: son's 81-GL, dtr's '94-940, my 83-DL, 89-745(V8) and 98-S90. Also 77-MGB and some old motorcycles.