Preemptive Head Gasket Replacement & Timing Reseal?

I took my 2013 Prius into the dealer to diagnose a strange noise and vibration that appeared to be coming from the engine bay area.

They had a tough time pinning down a root cause, but ultimately concluded it was a broken damper plate between the engine and transmission.

Since they put so much time in to isolating it, and tried a few things, and the $2k price to fix it didn't necessarily bother my overly.

My issue is they called back after tearing out the engine and stated that my timing cover needs to be resealed and the head gasket looks to be needing replacement soon. I was fairly sure they had stated the EGR valves look good though. They recommended I do the work, and quoted me for another five hours of work, at a further $2k.

If the vehicle was still worth more I'd probably have eaten it, but I'm kind of wondering if it sounds reasonable for it to be needing such work, and at such a cost. I had also just replaced the exhaust manifold a few months back, and they charged $1,500 for that. It's kind of got me wondering what to expect next.

I figured that since it's already torn apart, if the price isn't reasonable I'd probably end up spending more to have it reassembled and disassembled again at another shop.

What sounds like the best course of action?

 

It's right at 135k miles. Thanks for the insight and recommendation. I'll bring it up with them, and take a look at your links.