The piston o-ring needs to be lubricated about every other year. If you need a good sprayer, SP Systems makes excellent 2 and 3 gallon sprayers with very nice wands/spray tip. They cost $60-90 though. Check amazon.

Here is one to look at. There are others to consider at Northern Tools as well. http://www.northerntool.com/shop/tools/product_200332331_200332331 Here is a link that might be useful: battery sprayer

We've had many different brands of pump sprayers' over the years (Chapin, Gilmour, Flo-master, Hudson). They've all given good service. We use different sprayers for different purposes (e.g, one sprayer for 'edibles', one for rose chemicals, one for herbicides , etc). Some of those are quite old but still work fine. We prefer poly tanks. Metal tanks - even stainless steel ones - will spring a leak eventually. We also prefer poly wands - they do tend to bend annoyingly, but they don't break like the metal ones can. If you take care of your tools, they will take care of you. After each use, we triple rinse the tanks and then spray about half a tank of clear water at pressure. As needed during the season - depending on what materials we are spraying - we clean the nozzles and head fittings with a toothpick (metal tools can scratch). We lubricate the pumps before the beginning of the season according to the directions.. We NEVER store spray materials in the sprayer tank - we use it all up. At the end of the season, we use an ammonia and water solution (1 cup/5 gallons) to thoroughly clean each of the garden sprayers. Supposedly, that solution will even remove tough herbicide residues. But we don't chance that - we reserve a separate sprayer for herbicides. Then we spray a tankful of clear water mixed with a tiny bit of oil, dry them out, and store them for the winter..

Just buy a piece of copper, brass or stainless tubing and use a couple brass unions to slice it in or thread the ends to fit your valve and tip. IMO it will get expensive buying a bunch of replacement parts. Tubing and unions are cheap. You can probably get the unions you need at an automotive parts house or you might find them and the tubing at a hardware store. Tubing can also be found at recycling yards at a very reasonable price.