Broken ferrite still usable?

As the question implies:

I got a few E-I cores lying around that have been broken due to various causes (...<cough> dropped <cough>...). Just wondering if it would be terribly detrimental re-using these cores by say glueing or taping them together. They still fit together well enough that you can't see the cracks.

Would leakage inductance be too excessive for use as a power transformer?

Thanks

I've always found super glue repairs them perfectly!. Yopu can't even see the join afterwards.