One of the most common plumbing related issues I find in homes is leaking toilet seals. About 20% of the homes I inspect have hidden moisture around the base of the toilet.  I have seen entire floors rotted out as a result of this type of problem. In that case the homeowner put down a sub floor over the wet floor and lifted the toilet up off the flange making the problem worst, got to love the do it yourselfers. Although it is difficult to see the early signs of this type of leak there are some indications that you might look for. One red flag might be if you can easily rock the toilet by placing one leg on either side and gently moving back and forth. A loose toilet is likely a leaking toilet. If you find a loose toilet be careful when you tighten it so you do not over tighten it and crack the base. Another indication of a past of present leak would be if the flooring near the base is rounded down under the bowl. This would be an indication of swollen/rotten flooring. Of course if the leak has been longstanding you might see a gray stain under the lino or loose/missing grout in the tile. The longer the leak is allowed to remain the worse the job will be to repair the problem. If anyone is intrested I can go into how to replace the toilet seal in another post.