My family is currently traveling in our campervan and reported some leakage near the main water tank. See photo below. It looks like a water filter to me. 
As all RV mechanics are booked out until the end of times, and it's weekend, I'd like to try to fix it myself, as they will be traveling past our house this weekend. 

First step is to figure out what exactly it is, based on my research it's a water / sediment filter, and it's either dirty, it is cracked, or the o-ring has worn out. As it's ~6 years old, I guess that's the case, so a replacement seems the most easy fix.

Where would I be able to buy a replacement as I don't know what to search for? And are there different sizes?

I'm pretty handy, but without seeing the actual thing, it's hard to investigate.