The following is a known problem on all pre-2000 Discovery coaches, and it may also be a problem on other years as well.
The problem is that the base of the shower is not adequately supported, which will eventually result in the shower's fiberglass floor developing hairline cracks, which eventually widen and leak.
If you remove the access door in front of your shower, you will find that the shower floor is supported by a small base of what appears to be 2x4's stood on their side. What appears to be happening is the stress along the edges of this base causes the fiberglass floor to eventually crack. Also, while you are looking under there, notice that the small plastic shower drain pipe is not supported, so it would be a good practice to avoid stepping near the shower drain.
The first symptom of an impending problem is what feels like a squishy floor. As the hairline cracks start to develop, you can feel them with your feet prior to their starting to leak.
Unfortunately, the failure of the shower floor takes several years to develop, long after the warranty has expired, and Fleetwood will not repair this for free. Also note that Fleetwood recommends replacement of the shower base as the only viable solution. There are several alternative repairs for those of you not wishing to replace the base. In an emergency, duct tape can be used to temporarily stop leaks. A more permanent fix is to use some clear sealant, and you can find some good products at a marine supply store.
Several D owners have tried various solutions to provide reinforcement to the shower floor, with varied results, but the key is to provide a solid base that distributes the load over a wide area.
The DISCOVERY OWNERS ASSOCIATION, INC, was formed to promote the sharing of information and the camraderie of fellow Discovery motorhome owners. Membership in the club is limited to owners of Fleetwood Discovery motorhomes.