As u have three O rings two are quite large, so maybe it’s to retain them on the pump before fitting LR recommends Loctite 405 which is a cyanoacrylate glue, (instant super glue) there are equivalents to the 405 if you find it difficult to find it in Greece, Loctite 406 is a standard super glue.
So I’ll leave you to look at Loctite’s and site to find why LR states use 405. Possible the area/environment the glue will be use in, you don’t want to return because the O ring has moved and there’s a leak because u used something not suitable.
If any of the fixing bolts go into the water jacket then a water resistant thread sealer should be used there.