What model and year is this omc drive leg?
The newer models can be changed over to a volvo leg useing a transom shield adaptor plate supplyed by Volvo.
If it is one of the older models (a large rubber gasket on the transom cut out)than im afraid you are out of luck.
Am curious as to why three gear failures. Is it possable the drive leg gear ratio is not approiate for the application?
Hope this of some help