HP 28S is very loud when opening/closing

[RK_]

I have just received an HP 28S that belonged to my uncle. It hasn't been used in sometime, and when I fold it open or closed it makes quite a squeaking noise. I am not afraid the calculator will break each time I open it, but it does seem like something I should address. The hinges are tight enough that when you open the calculator it will not simply lay flat on the table without more adjustment.

I am not sure if I will cause damage to the calculator if I add some oil around the hinges, or if that will stop the noise.

I would greatly appreciate any suggestions or other tips about this calculator!
Thanks,
RK