There are two problems that the steering boxes on our 116s and 107s are subject to. The first relates to the leakage of oil from seals that have gone hard, and this is quite easy to rectify by disassembling the unit and resealing it. More often than not, you are supplied with an exchange unit, and whilst it has been resealed, there is very little control one has over the quality of the exchange unit from a mechanical point of view.
How often have you heard that "sure, the box doesn't leak...