so an update on the nipples , good news , after watching a couple of tricks on you tube , one being to put a socket end on and then tap the socket a few times first to help loosen and another tip was to use either a drill shank or a nail shank ( cut down to suit ) i found an old busted drill bit that snugly fits the nipple hole to help strengthen the hollow before trying to undo , well along with spraying plus gas the night before and the above tricks , managed to successfully undo all nipples without any damage at all
after undoing i worked them back and forth plenty 1/8 turn on/off to exercise the nipple thread.
im now going to wait until the weather is dryer and warmer as brake fluid absorbs water easily and my garage is unheated and inclined to be damp , so now ive freed them up , ill wait a couple of months before renewing fluid but ill exercise the nipple threads once a month to keep them from locking up again.
well pleased ! cheers guys