In my experience, vacuum boosters either work or they don't, with a rare bit of in-between shenanigans that are not similar to your issue . . . such as this one: https://www.gmforum.com/buick-172/co...-miles-311917/

I've never seen one reliably work slightly less hard than it used to. If they start doing something like this, their performance usually degrades quickly.

Let us know what the fluid level looks like.

Scanning it for ABS codes would be a good idea and when was the last time the brake fluid was bled?
Old brake fluid could have moisture content and a brake fluid test strip will indicate the copper content/ true condition.

Will mu OBD 1 show ABS codes?

Here'* how you get the system to give you any trouble codes.