Hi Ian,
I'm not certain this will help but I thought I'd share my story with my RX400h. (After finding so much help when I was looking for a car)
October 2017 and my wife wants to replace her car. She uses it mainly around town and drives to work 3 times per week. We also do the occasional long trip to the continent. We wanted a spacious and comfortable car for the longer trips for 2 adults and two teenagers. It also needed to be slightly higher up than a normal car. We started looking at standard SUVs (Nissan Quasqhai etc) but weren't keen.We decided the best bet was to go upmarket, looking for something older to fit our budget but still reliable. After much research we narrowed it down to the Lexus RX400h or Volvo XC60 . Why not the Volvo? - well nearly all were diesels and after issues with DPF previously we wanted a petrol, so the Lexus it was.
We knew we'd most likely be looking at a car with 100,000 miles plus and over 10 years old. To be honest there was a lot of dross out there. Many with the timing belts not being changed ("I'm certain it's been done but I've lost the paperwork..."), tatty interiors (torn seats) etc. After much searching we found a decent private sale with 131,000 miles, full service history but it needed a service. It had minor things needed doing (Roof bars needed powder coating, some interior trim replacing ) but really just needed a good clean. The main thing was the timing belt and water pump was done at 100k.
I can appreciate the concern with the hybrid but I think the technology is pretty robust and talking to my indie (Toyoda Tech) you're more likely to have other issues than the hybrid battery. If the hybrid does go (from my understanding) you can replace it but it's not cheap (used battery on ebay £600). However,compared to the cost of replacing parts on Mercs (SBC brake unit in Mercs will fail at some point - £1,000 to replace) or Range Rovers / Volvos, this is pretty reasonable.
Either way just over 15 months later with 143,000 mile on the clock apart from the first main service the car has been perfect. It's ticked all the boxes being quiet comfortable and spacious. The only thing I've done is replace and upgrade the battery (£54 Yuasa 48ah) due to some strange system warnings come up when it's cold. Once changed no more issues.
I'm also a Merc fan and have a CLS500 but annoyingly the kids now always ask to go in their mum's car! The only downside is it's not great on petrol but then again compared to the Merc it's positively economical.
My advice would be don't be rushed in to buying something, make sure it's got a good service history and find a good local indie (Toyoda Tech have been great ..) Maybe we've been lucky but I'd not hesitate in getting another. Your 100K car I'd look for a local Toyota/Lexus Indie to look it over.