Not likely, it's hard to get to enough without trying to work on it in place.
If you really wanna enjoy severe adventure then why not ..... You cannot fix it without taking your bike off.
See “How to remove the rear brake master cylinder on a GL1500 Goldwing the easy way” on YouTube by gosolobox(?). This will at least allow you to remove it the easiest way possible w/the least take down. I need to change the reservoir to MC fill hose & figure it might be time for MC rebuild as long as I’m this close. Job is no fun, but this method by far the best I’ve found.
That is a pretty accurate statement, it is said Honda started with the rear master cylinder suspended in air and built the bike around it.