Not on a Skyline, but on my "who gives a fk" 4wd, I found said cracks so used a CA glue and filler [ok superglue and baking powder but maybe fancier, who knows].
Fan was still going fine many years later when I sold it, inspected when I replaced the HB and it was all still together then, was actually impressed with my cheap arsed fix :), wasn't sure it would last that long, but it was fine.