Symptoms can very. The gasket helps keeps the combustion chamber, oilways and waterways all separate, therefore depending on which bit has failed will show as a different symptom. As has been suggested, you can get mayonaise on the oil filler cap, however you can also get also get oil appearing in the in the expansion tank. Other indicators are clouds of steam appearing from the exhaust, especially on a cold morning.
A couple of suggestions to help verify are to buy a compression guage and test each cylinder, this will indicate any loss of cylinder pressure. Also you could get your local garage to test for exhaust gases appearing in the expansion tank. All they do is remove the water cap and put over it a vessel containing a special coloured liquid. With the engine running and the liquid will change colour if there are exhaust gases present.
Then the twitch in your wallet can be confirmed as a serious case or mere anxiety. wink