is there anything that can be done to prevent the cover from leaking oil without much disassembly?

 

 

are there any specific additives that can be used to add in between a oil change? or is all the store shelf additives really just snake oil ?

 

Think about how gaskets and seals wear. Some is due to constant heat cycles where 2 surfaces expand and contract at different times . Some are due to the gasket or seal drying out. Also the fasteners can become lose after years of vibration. So the net is there is no way of telling how long they will stay sealed . Some of the snake oil stuff will try to soften the rubber seals and some of the stuff will plug the leaks. This is a short term fix and dependent on how bad the leak is it may not work. So I would say if you want to spend the money to replace the gasket before it leaks then it's up to you but there is a possibility that you may induce a leak because of a bad repair . There is also no data that gives you the mileage or years that a leak starts. So use the old adage of if it ain't broke then don't fix it.

 

The timing chain cover uses a high strength sealant/adhesive gasket material. Leaks usually caused by lack of full coverage during engine assembly. There are four critical areas that have been problematic as well. The crankshaft pulley seal (Garlock type) could be a source of an oil leak on high mileage cars but they usually last the life of the engine on most cars. The remove and install procedure for the timing chain cover is here: https://marclabranche.com/V6MR2/2GRF...20sub-assy.pdf

 

How bad is the leak? Or ES350 has the timing cover leak issue but it's more of a seepage than a leak. I discovered the seepage at about 80K, which the 70K powertrain warranty might have covered. I switched to a thicker viscosity oil - 10/30 which significantly reduced the seepage. The engine has never needed make-up oil and oil has never leaked to the ground. Engine now has over 200K and running well otherwise. I use full synthetic oil (Mobil 1 extended performance 10/30) and replace at 10K intervals. Only on the last oil change did I use an additive - Rislone Nano Prime oil additive, which is not designed to reduce leaks but to coat metal parts with nano molecules which could result in better mpg's - we'll see about that ...

Tacoma 2005-2006 V6 engines have a leaking timing cover issue also - TSB-0326-08. Many have succeeded in stopping the leak by coating the leak area with RTV. See post #9:
https://www.tacomaworld.com/threads/...eaking.562585/

On the ES350, the leak may be hard to get to - I can't see it in our car.