I noticed a hole in the engine coolant bottle of my 1992 240 the other day. Is this a problem?

There is a metal strap arrangement that holds the plastic bottle secure. The hole is right there on top where the strap crosses. I'm not sure how big it is because it seems to be partially covered by the metal strap. The part of the hole I can see is half-moon shaped and about a half inch long. It may be bigger if it continues under the metal (I haven't yet loosened the thing to check).

Now, I'm just an English major, but aren't car cooling systems pressuzized? And, if so, wouldn't this tend to mess up the pressure? I have never driven this car in hot weather. I picked it up last winter and it's still relatively cool here in Northern Wisconsin. No evidence of any overheating yet -- the needle on the coolant guage always moves about half way up and then stays there.

FCP Groton wants $24 for part # 9142000, which they call an "expansion tank," and I'm assuming that's the thing I'm talking about. Seems like a lot for what's essentially a glorified plastic milk jug. In fact, it's probably made from recycled plastic milk jugs. On the other hand, it's a cheap fix to head off a potential overheating problem.

Advice?

Pete