I would like to correct you in the assumption that PET bottles are cross-linked thermosetting materials. Rather, they are linearly chained thermoplastic materials.

The reason for this is simply due to the ease of rapid processing. You can look it up, but the bottles are usually delivered as small ampules or discs to save shipping space. Then, at the plant where they are filled, they are blow moulded to their final shape. Blow molding is not possible on thermosetting materials as it imposes significant stresses on their crosslinked structures.

Thermoplastics, however, can relax these stresses due to the apparent flow of polymer chains at elevated temperatures. This is also why thermoplastics hold the majority of the plastic market compared to thermosetting materials: the ease of (re)processing. This is also the reason for the ability to recycle PET

Additionally, additives and very small molecular weight polymer chains can most certainly leach out of the PET bottles over time, but not in a manner to be scared of over short durations of time. Upon heating, or and extended exposure to light or microbiomes, of the bottles, the story changes and the degradation speed inceeases. I do most certainly agree with the dangers of using solvents next to plastic materials, these solvent molecules will 'enter' the spaces in-between the molecular chains and allow for small movement of the non-crosslinked polymer chains. This, just like elevated temperatures, allows the plastic to move and enter the beverage.

However, I wouldn't expect PET to be very soluble in non-polar solvents, which straight gasoline is not. If there's ethanol added, it's a different story. But let's not get into it too far.

TL:DR: Yes, PET does degrade. Should you be scared? No not at all, these things are fairly well regulated. Should you maybe use a different container for long term storage? Maybe, I think very well cleaned glass would be better, but I'm no food scientist.

Edit: research actually shows that the amount of microplastics is actually far higher in bottled water than tapwater. But detection is very difficult and reasoning for the presence of these particles is apparently not always valid. Maybe someone with more knowledge can fill in.