The problem with these pumps is that there are hundreds of them that have been lying around for years and you dont know what people have done to them proviously. You should be able to turn the pump fairly easily by hand, but in any case I would not consider using the pump without dismantling and cleaning. It is easy to dismantle, but it is important to mark each gear, because they need to be re fitted in exactly the same position, I was once told that they should even be fitted into the same gear mesh. The pump itself is very simple but the problem is wear to the end plate and drive. If the wear is excessive this will allow oil to leak past the end plate or through the drive spindle which will cause a drop in oil pressure and also cause wet sumping which is another story. So dismantle it very very carefuly and see what you have got. all the best.