From the color, the dark band on one side and from your description that it has leaked it could be a tantalum capacitor.
In that case "B" means either the size (L=3,5mm, B=2,8mm, H=2,1mm) or is a code for the voltage.
As to the number 450 I'm at a loss. Normally these components are labeled with a 3-digit code where the first two numbers give the mantissa and the third digit gives the exponent, all in pF. Thus 450 would be 45*10^0pF=45pF which is nonsensical for a tantalum capacitor.
Are there any other inscriptions that could help?