We would need to know the type of nickel plating used on these components. If you used sulfamate or electroless nickel, soldering would be the best way to go.
Electro-Coatings
http://www.electro-coatings.com
If you’re looking for both abrasion resistance and corrosion resistance, hard chrome electroplating or electroless nickel might work. Either one will change the dimensions of the fitting slightly (adds a few thousandths to the component), but it will be substantially more durable and resistant...