Looking For Replacement For Keyed Exterior Patio Mortise Lock And Keeper

I have an old mortise lock on a sliding patio door which no longer seems to function properly to engage with the keeper. It is a keyed exterior lock. Photos show the keeper, the exterior of the lock and the interior of the lock. Outside it locks with a key. Inside it uses a little slide mechanism that goes up for lock and down for unlock. I'm not sure what's wrong with the mortise that it no longer engages with the keeper, or it might not ever have properly engaged or fit that keeper. The length of the entire item from top to bottom is about 7 1/4 long. No name or brand on it...as you can see it is pretty old! I need a replacement of this item to be able to lock the door from the outside, as well as the proper keeper or a set that matches so I don't buy the wrong keeper or guess at the type of keeper this unit needs. Any help would be appreciated!

I've added two photos of the latch mechanism, with the latch in the "up" position and the "down" position. This is what is not catching the keeper, or easily pulling away from the keeper with a little tugging on the door, so it can't be used anymore as a safe locking device.