Got a helpful body to sit on the back rack again, trying to see if the chain tension is a problem. Got him to put his boot on the tensioner to really tension it. Did this or the oil change help? Nope.
Talked with guys at Cheeky Monkey to see if they had any further suggestions on the plan of attach, and to give them the heads up if didn't have any joy after trying on my own. I also talked with Maria at Rohloff Australia She was very helpful; suggesting what to look at that have caused people problems in the past; chains, sprockets, joiner links, overly tight or loose nut tensions, etc.
The slipping I'm having only happens with heavy load on. It didn't happen when I had the hub in the MTB touring. One reason I'm still going to change the tensioner and look at chains and sprockets. On the MTB I didn't run a tensioner- having slotted dropouts, so could move the wheel back. Load on the MTB rack was probably in the 40kg range. I figured my two loaded Go-Getters were in the 60-80kg range. My helpful body load is over 100kg. He wouldn't say how heavy he is, but was socked when I asked if he is less than the 200kg Mundo rack limit. He assures me he is :)
Result: I'm going to try all the easy stuff first; changing the chain tensioner to a Rohloff one. I'll get two new chains, no half or joiner link, and new chain ring and sprocket. (well swap them around). If that gives no joy, then will send the hub back to Rohloff to have a look at under warranty.
Tracked down a torque wrench and spent some time this afternoon checking bolts that I've touched on the external gear mech, OEM adaptor plate, and axle nuts. Found I had everything too loose. Wasn't that surprised on the smaller bolts - I was worried about doing damage making them too tight without the torque wrench. The axle nuts - I was surprised how tight they get done up. I've had problems with the nuts working loose before - so guess now they are tight. Will wait for the tensioner and new chains before trying a heavy load again.
Also had a go with the oxy - and plugged up one leak in the frame. What's this about? I put all stainless button head bolts with washers in all the braze-on's on the Mundo - to stop water entry. There are lots of them, which is really handy. As I was doing this I squirted some light oil in the frame. I noticed that it leaked out of two on the rack. It looked like that when the weld went around the tube, they missed by pin prick meeting up to the start of the weld. A drop of braze to plug it up. I put some more oil in after this, but found I missed sealing one of them. Will do that one again tomorrow.
Back to waiting on parts to arrive, before testing it all. In the mean time - time to go riding.