parts are readily available from casa and in banawe. of course, there would be some hard to find parts which may require to be ordered from germany so it usually takes 2 weeks before delivery. for typical parts required for preventive maintenance, it is easily obtainable from the said sources.
also, there is a guy selling opel parts in the opel forum which can deliver to you any part in only 3 days and his prices are cheaper than in banawe.
I had a Vectra wagon V6 for 3 years. The car felt rock solid, as a German car should feel, and the engine was smooth, torquey and powerful. Generally stable at very high speed - in a straight line, because handling though was quite poor. My problem was with the totally crappy service of GM Phils. The worst! Crap talaga! They made a car that had some problems emerge from normal use even worse, poor car! Once a transmission cable gave, after just two years, and it took three weeks to get a replacement! Another time I sent it to them for a coolant leak, and in the course of fixing it they created an oil leak, for which it had to be towed back and fixed again. For the long hours waiting for a tow truck in the middle of the night, for the missed family vacations that had been previously planned but cancelled because the car had to go in to fix something THEY caused, for the missed meetings, for running without aircon in the rain because they could not fix a simple temperature sensor after three tries, etc, etc, I swore never again to consider a GM car. It was okay when it was working right, but it just had too many problems aggravated by poor service.
However, two years ago I used a Vauxhall Astra (same as the Opel Astra) as a rental car in New Zealand for eight days. It was very nice to drive, good handling, good engine, and just as solidly built as my Vectra. I should add though that it was brand new when I used it.