I did some research on what can cause this and a few things came up.
1. is the machine level? Although I would rule this out as most floors are. I had to add this.
2. Detergent can cause suds which can cause leaks. Again I assume you used the correct type for dishwasher.
3. If you have not used this for a while, several things come to mind. Was the unit stored in the house living area or in a basement garage or other unconditioned space. Higher then or lower then normal temps can mess a machine up fast. With a machine that holds a small amount of water in its pump once it is first used can crack if it goes below freezing during cold months. Hoses also dry out in extreme heat or cold. Rubber seals dry out over time resulting in leaks also. So the list is really endless.
As far as fixing, sure you can fix anything. But portable units are fairly inexpensive and your model appears to be a bit older perhaps mid 90s. Repairing this unit is not worth the cost of the parts or the time. Even if you do it yourself.
If your still game however to give it a go, you need to remove the covers to gain access to see exactly were the leak is coming from. As there are a lot of things that can leak. From hoses, gaskets, cracked parts, faulty door seals. pump failures, clogged screens.
Oh my gosh, Woodbridge Environmental, that I did not answer.......... I believe you are so very correct on at least 3 topics....... I did not use if for way too long, so I believe those rubber parts just got hard and died...... I mean..... who wouldn't? lol
I have not tossed it YET, but will be moving it out to the carport or close enough to see if it is even usable at this point........ I doubt it. I was told before to run a dishwasher at least once a week......... oh dear .... I have not. I guess they hated me when I lived in an apartment complex.... I just never got into using them..... now I am so very regretting this sad flaw.
I let this happen to my full size dishwasher, mainly because I went for so many years without one that when I installed one I was accustomed to using it. I could kick myself though. Curious after a year what you have done?
Oh gosh, I have done nothing. I too, did not use it like I should have.... sad huh?