There may be a bug in CR 2008 that fails to read previously available Custom UFL Functions. I have tried this on two separate PC’s that have multiple versions of CR installed side-by-side and get the same result. In CRv12 the node for Visual Basic user functions (u2lcom.dll) doesn’t show up in the function tree under “Additional Functions”. However on that same PC those functions do appear in all previous versions of Crystal. I am also checking in with some colleagues who (so far) are finding the same behavior.
If you get a different behavior please let me know. And if your reports rely heavily on UFL functions you may want to confirm that your functions work in CR2008 before you lock in on the upgrade.