I replaced mine a few years ago because water in it froze and broke it. Pretty easy, just a few hose connections and a small amount of coolant spill when disconnecting those lines (plug 'em fast!). I don't know much about the design, but I think a brazed plate heat exchanger designed for domestic use keeps the liquids separated. Here's a few links with info you and other members will find interesting:
Lots of size options on McMaster's:
The Kelvion website describes a particular design series (https://www.kelvion.com/products/product/gb-dw-series/
) that is described as "consist of double-walled, hermetically sealed plates. The system convinces with two stainless steel plates instead of one, at which the second wall not only separates the media from each other, but also makes the leak visible. Thus, the mixing of the media of primary and secondary side in case of a leakage should be prevented".