Elkrig, thanks for sharing and too bad to hear about these issues. I kind of hoped this was more so for US made 5.7ltr V8's (3UR-FE) and vehicles like the Tundra and Sequoia than Japan made Land Cruisers. So does not seem to be the case, although I hope it is less common... Whether this is lemon or Toyota should fix outside warranty I do not know. Lemon for a vehicle which is 2013 and 98k miles seems unlikely, making Toyota to step in is worth trying.
Regarding your issues, the Care Care Nut (AMD, ex Toyota Master Technician which seems to genuinely give good advise) actually did a repair on these issues on a 2016 Tundra and posted a video on this recently. While lengthy, he makes some statements on parts to replace or not.
Categorizing in must do and good to do, without being the expert, just summarizing what he is saying from memory and adding my interpretation so take it with a grain of salt:
- Valley coolant leak; seems must do or it just gets worse and leads to cooling issues. He indicates seal area on valley coolant chamber is not wide enough and becomes an issue at some point on the 3UR-FE. May have to do with proper cleanliness of the seal area during original manufacture assembly. I had hoped in Japan they do it perfect... Overall does not seem you can do much about prevention, it just happens
- Cam tower leak; depending on how bad a must or good to do. He suggest wiping the area and monitoring the leak rate is a step to consider. If it is worse which is maybe your case then have it fixed
- Timing cover leak; probably the same as cam tower leak, must or good to do
- Replacing Timing Chain Tensioners; Do not know if they get bad on 2013 Japan made 3UR-FE's. They certainly are an issue on the 16 Tundra he is working on. Seems good to do as you are in there
- Chains and chain guides; Should be fine if the chain tensioners are not bad yet and there is no noise from the same
- Water pump and thermostat; Good to do as you do all these repairs. Items known to go out.
All in all once you are in there it is worth considering doing the whole lot. Getting genuine Toyota parts and latest version of the same seems valuable. By doing so you should be good for another 100k miles +
In case you are looking for long term ownership it is worth considering switching from 0W20 to 5W30. Also doing it every 5000 miles as it apparently keeps things cleaner and running better. I can see Chain Tensioners working better over the long haul.
Maybe AMD in Chicago is an alternative option from a South Dakota Toyota dealer. All depends on delta cost (assume AMD is competitive) and how much effort you want to put in (travel to AMD shop and back). Looks like the Tundra repair was around $5.5k, so it adds up.
Keep us posted what you do and possible by whom and how much.
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Removed youtube link, see above from Texas Meatball...