So, Abacus had the car for some other work and looked at this while they were at it. They said it's definitely a lifter not pressurizing as quickly as it should and they blame it on my low idle when cold. That answer doesn't really satisfy me because it does it longer the colder it is out, and it's only one valve (I have it narrowed down to one of the two valves for cylinder 7).

How bad is it to leave it like this? The lifter is only $50, but the tools I need to change it (MB proprietary valve spring compressor and go-no-go gauge) are $260. Will waiting until mid-January when I have the money hurt anything?