As far as I can remember Rudland Rigg isn't really a problem. The Southern section, as far as the old railway, can be driven in anything (I've driven it several times in a Transit). Just north of that there is a patch of clay that gets muddy but shouldn't stop you. The northern section down the bank gets very eroded during the winter, and you need a bit of care to avoid large rocks and potholes. The two side tracks going down to Church Houses and Cockayne are steep but a friend took a brand new RR up and down them about 20 years ago with no incident. Don't know how they have fared since.
Further west, the track down from New Row to Guisborough is fun, but if the forest track alongside isn't open the downhill bit of the right of way may give you a few scratches. We took a VW bus down it once, and found little piles of mud on the front bumper and driver's door handle. Not sure the seats smelled the same afterwards either.

rudland rigg was very easy going for the freelnader, we started on the south side and worked up just over half way i guess untill you get to some cross roads, turn left down a track with 3 gates using hill descent. at the road turn right and then through the next gate on your right. this takes you through a woodland section and is fine all the way to the top where you have an option of going back to the moors on your right which is nice and easy or left furhter into the woodland which we took. heading down is ok but once over the stream and heading back up the other side the track starts to become rutted, muddy and narrower.

My car looked like yours doctor but just did not show up on the pictures and funnily enough we had a rattle sound up to about 50mph for a good 5 minutes on the way home, gone now though.Wahed it tonight with a jet wash and covered the drive ( and the neighbours ) in mud and clay. no way would i have been able to get the mud from underneath with only a normal hose pipe though.

Recommend it Toeknee for a great 'free' day out  freelander 2 SE black and beige - now sold

I can't quite square that with the actual right of way. From what you have written, I think you turned left after the railway crossing and maybe went down the old railway incline. If it was straight and a regular gradient, that's what you did. The right of way (drove road) carries straight on along the Cleveland Way, only starting to dip where the Way veers off to the right along thew contour. You then hit "Turkey Nab", which is a set of hairpins down the steep bank, which as I said can get very eroded overv the winter. I've walked down it, and also drove it once in a Series 3 LWB. I wouldn't describe it as easy, although it's doable with care. This brings you through a short stretch of wood to bank foot, and the road into Ingleby Grenhow. Agree that it's a good route, with the advantage of being a "through trip".