You will find many posts on this subject under the heading, ‘Bavaria Through Hull Valves’, on page 2 of the General Section.
We posted several times on this subject. One of the problems with the Forum is that there is no convenient way of keeping all posts on the same subject together. The only way I manage not to miss posts of interest to me is to check the site about once every two weeks.
You will see that we came to the conclusion that the actual skin fittings were bronze and in good condition, but chose to replace the ball valves as, like yours they had become stiff to use due to the pitting that we found on the plated surface of the balls. We also replaced the hose tailpipes as these were ordinary brass. The supplier we used is detailed in our posts.
Hope this is of some help.