1995 250hp repair questions

[libbylou]

Just purchased boat W/ 1995 250. Mech did the following, carbs rebuilt, fuel pumps rebuilt, replaced throttle sensor, water pump & thermostats replaced,good compression. First trip motor ran good except for overheat buzzer during idle. I removed head & exhaust, cleaned salt build up and replaced gaskets. Put motor on hose and got overheat buzzer twice after a few mins. First time I didn' hear it due to engine noise and it did get hot. Was told this engine would not run cool on a hose. Took to lake and motor didn't overheat, but ran rough with definite miss & fluctuating RPMs. Friend said I might have blown head gasket when it overheated on hose. No signs of water leaking around head, took plugs out and no sign of water. How can I tell if I have blown the gasket without disassembling? If I disassemble, would you reuse the new gasket the second time? Do you use a sealant on head gaskets? Any other suggestions for the DYI.
Thanks

[boats.net]

Run a compression test to see if compression is even on all cylinders, don't reuse head gaskets and don't use sealant on them.