When I went to take out this upper left bolt it was feeling really tight, then "rubbery", then the head broke off ... I tried "liquid Wrench" with a nut on the end taping it a bunch with a hammer to "induce vibration" gripping it real tight with needle nose vice grips, etc. and letting it baste for a couple of days.. SO I thought maybe I could use it as a stud with a sleeve nut and it torqued down good.
https://www.ultimatesubaru.org/forum/gallery/album/897-ea82-water-pump-broken-bolt-fix/