If you haven't blown any oil seals or gaskets, you should be ok. That tube is the breather tube and that is where the extra oil will go. Since the CRF450 doesn't hold very much oil I run my oil level all the way to the top of the sight glass. So far, no problems.
It's a good idea to change the filter often. Also, inspect the filter closely. If there are any problems in the engine you will see small metal particles in the filter.
Check with your local auto parts store on the filter. Fram is supplying some of the smaller filters to them.
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