Some spa and hot tub manufacturers are offering Ozone generators and/or Salt Water systems to sanitize the water. Although beneficial to water quality, salt and ozone can be detrimental to equipment like standard heater elements and standard pump seals.
These heater elements are more expensive, being made from Titanium and all… but if you’re replacing a standard element every 1-2 years, there can be a quick payback in a few years. The ozone grade pump shaft seals are only a few dollars more than standard grade.
So, if your spa heating element look deteriorated and corroded, and you use salt and/or ozone to sanitize, my recommendation is to replace with a version that can withstand the salts in the water.
If your shaft seal is failing, and you use ozone in the water, look for a softening and puckering of the rubber portions of the shaft seal, or possibly corrosion on the spring portion.