Compared to the M30, a valve tick isn't a big deal on the M42. I'd presume it's just a sticky lifter. A little synthetic 5w30 might clean that up. If not, there's no need to pull the motor and drive the lifter shafts & cam out of the back of the head...the M42 cam trays simply lift out.
The things you'd urgently need to check on the M42 are the upper oil pan bolts, the profile gasket, and the cam drive gears.
The cabrio is a lovely machine. The manual top is a great option, it doesn't break like all the EM power tops do. The convertible is unfortunately about 300# heavier than the coupe & sedan. Despite the incredibly short 4.27 diff...this car (alas) will never be quick.