Maintenance of stovetop espresso makers

Stainless steel units are easier to maintain as aluminium ones tend to corrode from contact with water.  You can prevent this corrosion, though, by not allowing water to sit in the unit when not in use and making sure to clean and dry thoroughly after using.  Never allow these units to air-dry.  Store them dis-assembled as well, in case you missed a couple of drops of water while drying.  If drops get trapped in the unit, the corrosion will start.

Allowing a layer of coffee oils to build up on the walls of your aluminium moka pot is said to enhance the flavour, as well as provide a barrier between the aluminium and the coffee, for those worried about potential health risks of aluminium (research has yet to show any health risks from aluminium moka pots, but it is a concern for some people).  If you don't use the pot for a while, though, the coffee oils can go bad and you will want to wash them away and re-season before using again.

Inside the moka pot is a rubber gasket or o-ring that will need to be replaced periodically.  Keep an eye on it and watch for signs of deterioration.  If you wait too long, it becomes more difficult to remove so try to stay proactive.  Keep in mind that moka pots come in all shapes and sizes and so do their gaskets.  They are typically not interchangeable so when you buy the pot, check that the store also carries replacement parts or find out where else you can get them.  Make a note of the brand and model names as well as the size.

The filter plate and safety valve can also be replaced if needed so, again, find out in advance where you can get them.  Generally, the only other spare parts you might be able to get are handles so if you break a part of your pot, you may have to buy a whole new one.