Rovers tend to build up carbon on the valves. Some valves have a "carbon breaks" that traps the carbon so as not to allow the valve to pull it into the guides. But, at around 100k, you may notice hesitation at highway speeds. Unfortunately, cleaners brought in through the intake or fuel don't help much as they are burnt off before reaching the troubled exhaust valve. Seafoam might help if put in the oil. But, this is one of the few, continued head probs. Valves could be cleaned but the carbon can score the valve which in turn scores the guide. A valve job shouldn't cost more than a few hundred. I had this problem on a 68 Jeep cj 3. The stock engine. . . a buick dauntless v6- the sister to the rover block. When the valve stuck, it sounded and felt like someone was hitting the exhaust manifold with a sledge hammer. Wish I still had it.
