If stuck, I have used "Goop". Here in North America we have tubes of "Goop" available, in a few varieties. It has been analyzed and appears to actually be all the same, with the exception Outdoor/garden Goop, which may have UV inhibiters in it. There is Marine Goop, Plumbers' Goop, and I think, Shoe Goop. It is a thick clear "Stuff" which seems to bond the plastic of the B'mann railings. If used sparingly, it won't show too much. The metal replacement railings are great, but are rather pricey...
There was some shop or firm over in Britain offering some grabs and railings for the B'mann bobber caboose at one time...I don't remember who he/it was...I wonder if they made any other offerings.
Fred Mills