I had a similar problem with my disco ,I changed the lift pump & it felt smoother but the starting issue was still there. I put a new battery on & now it starts first time.
Yes Dayco is OEM, not worth the hassle fitting the cheap part. My chirp came back instantly with the cheap ones but nothing with the Dayco . 20 min job on my 300 , 15mm ring spanner is all that's needed :)
With my headlights(300 disco) it takes about 2 mins to chance headlight & sidelight bulb. I just hit the bottom corner of the headlight and it pops out. Easy pips
Bulb has blown , the 2 outside knobs on the heater control unit . Pull them both off and you'll see some screws . Undo them and you'll see where to replace the bulbs.