Finally you found the culprit. A correct compresion test at the first instance would have saved you from so much of headache. Reduced compression pressure can be because of various reasons. If you can trace the real reason, maybe you can be saved from spending huge amounts.
At 1 lakh, piston rings going bad is a rare occurence, unless you have illtreated her during her lifetime. Since changing of piston rings requires dismantling the engine completely, I would suggest you few checks before you go for complete decarb or sell off your car.
- Please check the condition of engine oil. On touching, do you feel high carbon content (It will feel more viscous than oil under normal condition). If piston rings are gone, engine oil condition will give you clear picture.
- Another goof up could be bad adjustment of valve tappets. If clearance is less than recommended, the valves wont seal when temperature rises up, and you'll feel lack of power. Do consider rechecking of valve adjustment. This option will be much cheaper than piston ring renewal. Also after this test you'll be sure of your next step (sell/retain the car). But do get it done from a reliable place.
There could be few other reasons. But in your case, I feel these 2 or most relevant. And I very much feel, tappet adjustment would solve your problem.
Please note, if you run your car in this condition for prolonged time, the valve & seat are liable to get damaged, and you'll need to change/ lap them.