I knew of a 1.6 K Rover 45 with 250K miles on it.
It rattled a bit from the top end when started, but that could have been down to incorrect head gasket replacement, blocking the oil ways in the head (wrong sealer used), which is common.
I'm pretty sure that 45 had 3 HGs over it's life span, unfortunately it's not about any more, as it failed it's MOT on rust, and wasn't worth fixing due to the high mileage.
The K series isn't unreliable at all, HG issues excepted.
The design was and still is groundbreaking, unfortunately the materials needed to keep this advanced engine design sealed up tight weren't up to the job, so HG issues occurred.
However I don't think it's much hardship to replace the HG properly at say 70K intervals, as the rest of the engine is pretty indestructible.
For me, I think the K series is actually more reliable than that BMW sourced hunk of junk fitted to the TD4 FL1.
The K series is definitely cheaper to repair, when issues do crop up occasionally.