potential buyer - does the car have coolant issues?

I posted earlier in the newbie forum, but thought I'd get more responses here. Apologies for the cross-posting.

So I had a 2006 with 86k mi inspected today as due diligence before potentially purchasing. Unfortunately, the mechanic was not a specialist, but I went with him because he was vouched for by my girlfriend's family and as a bonus he is located conveniently close to the dealer. Anyway, he said almost everything looks great, no issues driving, super clean, the previous owners were good about maintenance.

However, he raised two issues:
1. Standard concerns about the longevity of the battery. I've just read up on this here (again), and I'm more or less convinced it's a small risk that I'm willing to take, on par with the risk involved buying any used car.

More importantly...

2. The coolant reservoir appeared to be empty, but there was no leak that he could find. Indeed, at the dealer's, I did not see evidence of a leak underneath the car. I'm puzzled about this one. Could this just be dealer negligence? Or a hidden leak somewhere? Both? If the coolant were low, shouldn't an alert have appeared?

I looked up the service records. Seems about a year/20,000 mi ago they replaced the following:

HOSE, RADIATOR, N TO16571210801
HOSE, RADIATOR, N TO16572210601
HOSE CLAMP TO501064
ANTIFREEZE GALLON TO002721LLAC011
THERMOSTAT TO90916030931
GASKET, WATER INL TO16325620101

Also, about 3 years ago, the check engine light came on. Here's the description:

CUSTOMER STATES CHECK ENGINE LIG HT ON WARNING LIGHT ~|~CODE P0A93 TSB ~|~R/R INVERTER WATER PUMP//CLEA R CODE

And parts replaced:
SUPER LONG LIFE C TO00272-SLLC2 1
PUMP ASSY, WATER TOG9020-47031 1

Apparently 'Super Long Life C' is Toyota's coolant. So looks like coolant issues have appeared previously. I'm worried that there is an internal leak that will be hard/expensive to diagnose, and that if left unaddressed could cause serious problems. Anyone experienced recurrent coolant issues?

 

My bad, sorry.