These "issues" are well known VBM quirks and have been discussed elsewhere,
The VBM represents brilliant value for money at the price and the difficulties are easily overcome. In comparison, a GS3 is almost perfect and is also $6.5k...I reckon you have done ok. What can it put in the cup?
Like most other machines, VBM are hand made and subject to small variations. I consider these variations to be optional extras which are not charged for. In addition, about 2 minutes of your time will overcome the majority of these issues.
Keep in mind that your supplier should have adjusted the OPV using a portafilter pressure gauge for you and as such, you shouldnt need to be inside the machine anyway as you probably dont have the equipment required to accurately gauge the effect of any adjustments :-?
Most espresso machine importers will be reluctant to provide warranty on machines which are user modified/damaged.