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 and if so should I ask for more than a 30 day warranty on the repair ? The shop typically issues a 30 day warranty. I didn't authorize the repair and probably wouldn't have because my own personal experience is hit and miss with these types of repairs, however i am not a pro when it comes to epoxy type patches. The bill covers muffler replacement ($500 part + $'s in labor for light modification due to inability to locate a replacement new/used), which caused the crack according to the mechanic, purging and bleeding hydraulic system as well as the tank repair. Thanks in advance for any help

Fiberglass repair to hydraulic reserve tank ?