ABS Cement works very well if you prep the broken piece properly. First make sure there isn't a lot of grit in the cracks, if so blow it out with an air hose then use some PVC type Cleaner to prep the joint.
At this point you can either use fresh ABS Cement to fill the crack from the back side or try some with a little Cleaner in it to thin it down for better flow.
Depending on the length of the cracks you may be able to cover the painted side, which will have some paint damage and leak through of the ABS Cement, with one of those 1 1/4" diam chrome plated mounting washers made for spreding the load.
On the other hand if the cracks are rather long and you are lucky with some Clear Packing Tape you may be able to tape over the painted side before applying the fresh ABS Cement to the back side and flex the lid just enough to force some deep enough to fill the crack without oozing out on the painted side enough to damage the paint. Kinda tricky but it can be done sometimes with little or no black line in the paint.
In any case with ABS Cement allow a week or more for it to set up fully in a warm room. You can also add an extra layer or two to the back side for strength which will add to the time needed for it to harden properly.
If you are going to re-paint then don't worry too much about the ABS Cement seeping through from the back side to the painted side but try to keep it minimal to make the following Paint Prep easier.
Another method of repair is the Hotcha Repair Kit
that was sold to repair the Vetter Fairings early on and is still available from various sources including Craig Vetter via;
I have used this kit on various ABS parts for the past 30+ years and it is the quickest way to repair parts or make attachments to ABS. However it is kinda expensive $$$$ which is why ABS Cement is the prefered method for those on a budget.