Coolant leak 3-4 yrs, now low oil pressure, after 3 times of having something fixed and still having problem, gave up and just been filling coolant, finally someone says it's a crack in the cylinder head. Would k&w block sealer be an option?

Head Gasket Sealers--How to pick the right one (http://www.ricksfreeautorepairadvice.com/category/cool-automotive-products-and-tools/head-gasket-sealers)

Does your block have Freese plugs, and have you checked them? And have you warmed the vehicle up and checked the exhaust for coolant? It should come out as steam. Also I would place a piece of cardboard under the motor and see if there was even a small leak some where and definetely check the bottom of engine for moisture.

Oh and by the way block sealers although handy in a pinch can cause a lot of headache later. I/E thermostate, heater core etc.