I came across it spelled [e+oo sh]. S90 Func Meth, Less 59, Para 594, last sentence, for those interested. I thought it might be a mistake in the book where the pen writer used an older form but it’s spelled the same way in my S90 Dictionary. Of course, it’s possible they could both be mistakes/inconsistencies in the texts but it seems odd there’d be a mistake in both.
Now ‘-tial’ somewhat resembles ‘-ual’ but I would’ve expected it to be spelled [e+oo sh u l]. And when I checked by DJ Dictionary it has it this way.
Finally, I checked my Simplified Dictionary and it has [oo sh].