GE had problems with their type U bushings mfg. in Pittsfield MA from 1958 to 1980. Typically you can perform a power factor test on the bushings and monitor the issue. Doble and ABB have published several articles on the subject.
GE type U were manufactured between 1954 to 1986 during that time GE accounted for 65-70% of the bushings manufactured for the US market.
The most well known problem with these bushings is the Rescon ink that was used as the capacitive layers to form the core. There are many problem with this design ranging from the ink, paper thickness, top can cover design etc...Mostly the problems lead to increasing power factor which leads to failure.
The Rescon ink core was not only used in type U bushings but also some type T's.
You can have these bushings repaired by a bushing manufacturer where a new core design will replace the troubled Rescon ink design. Both PCORE Electric and ABB offer repair services and are original equipment manufacturers of bushings.
As the above poster mentioned contacting Doble Engineering or ABB I am sure will provide you with some quick information.
