I've broken the filler cap on my makita leaf blower, innards are OK but the crew cap has parted from the end cap, one on ebay has the same problem so it may be generic. I effected a temporay repair with a soldering iron welding the plastic but that failed after several fillings.
So I'm looking at casting my own and need to decide what to use and what to strengthen it with, Plan is to wrap the neck in cling film and cast over that, appearance is not important.
AJH