I'd drill it out and replace the full piece, including cutting the new angle. Acrylic is easy to glue with Weld-0n #3 (once you've practiced), but this will probably take more effort and save little as you'll have to buy as 6-ft length of acrylic tube (shortest length if ever found) and you'll have to find a local plastics distributor or ship it with the Weld-On solvent. You could sleeve the inside, but it would reduce the flow which isn't ideal, and unless you are already significantly oversized with this skimmer, would result in undersizing. If you do use an inner sleeve, use as thin as will hold up to the constant vibration. Glue with Weld-on #3 (plastics distributor) or pvc glue may work but not as strong.
If however he has the full broken piece, you could put a collar on the outside and redrill and replace with larger uniseal. That's the best approach if you can do it. Go slow with cheap "diamond" bits from eBay for coring. Heat is your enemy, so consider drilling wet. Alignment will be critical so use a predrilled guide that you've secured, after marking, or some other way to ensure alignment.
This would probably at least $100 mostly due to the acrylic tube, and at least 2-3 hours of frustration.
In short, if you have time and want to learn how to glue acrylic (I do all my own sump mods, to very good tailored results, but had leaks until I learned better, and it doesn't always look pretty), it's a good project, but it won't likely save you much and your repair could very possibly fail a few times until you get better at it. I'd probably do it, but I'm a glutton for punishment. One thing, you'll need to be handy to have any chance of success.
Let us know how you make out.
