Rover 214 SI handbrake lever

Hi all, I need some suggestions about the handbrake lever of a 214 SI (1994). When lifting the lever , the push-button doesn¢t perfectly return in its rest position, causing the lever not to stay upwards . I think it¢s only matter of lubrication or grease. But unfortunately, even dismantling the whole leverage

I didn¢t find any good way to put oil or grease to the push-button internal spring. The reason of this is that the plastic triangular cover can¢t be moved because the black plastic handle is too hard to extract.So everything is up to that handle...What could it be the right way to disassemble it? TNX in advance

Paolo