Fiberglass repair to hydraulic reserve tank ?

I need some help/advice/opinion about a repair I had done to my early 90's Mustang 930A. It had a leak, hydraulic oil coming from the reserve tank (tank behind the seat). The shop I took the machine to repaired it with a fiberglass patch. The couldn't find a replacement tank new or used and it was cracked around the fitting. The tank wasnt metal so it couldnt be welded. I feel uncomfortable with the fiberglass repair and the bill is $1950. Is a fiberglass patch typical for this type of thing...

Fiberglass repair to hydraulic reserve tank ?

Fiberglass repair to hydraulic reserve tank ?