The ProLine is probably made by either Britpart, Allmakes, Bearmach, or NRF. I got one by Britpart here: UTP1725 | HEATER MATRIX STRAIGHT PIPES DEF | Britpart | Defender 1983 To 2006 | Britcar (UK) Ltd
. I figure if it leaks it was cheap enough I could just get another. I'm sure they're fine though.
------ Follow up post added February 25th, 2015 10:44 PM ------
Here's one sold by Amazon. They always seem to be great with returns. Also, the price includes VAT, so it'll be even less after you select a US delivery address.