Can you tell me what is wrong with my car and whether it’s worth fixing.

It’s a Vauxhall (Opel) corsa D, 2009, 142,000 miles.
I have owned it since 2018 where it had 60,000 miles on it. I am based in the UK England.

So far I have done the following works to it over the years.

- new A/c compressor
- new clutch
- new alternator
-recently new coil pack and spark plugs due to misfiring
- new rear silencer as it fell off due to rust
- changed rocker cover gasket
- new oil pressure switch
-changed oxygen and crankshaft sensor

Now the heater is only blowing out lukewarm air not hot like it used to.

I took it to a mechanic who looked at it for free and he said the following (not sure if it’s accurate).

- doesn’t think it’s head gasket as there’s no white smoke from the exhaust, engine is not cranking when I start the car (starts first time).

- he felt the two pipes in the engine bay and one was hotter than the other ( so it could be a circulation issue)

- he touched the coolant with his hands and said it looks like something is mixing with the coolant. Could be oil or could be something someone who owned the car before me has added into the coolant (sealant of some sort).

- said it could be water pump as that circulates the coolant around the engine. Timing chain is making a ticking noise and rattling on cold start so advised if changing the water pump might as well change timing chain also. Quoted me £500 for timing chain and water pump with parts and labour or £250/300 for labour only if I buy the parts.

- said could try bleeding the cooling system and adding new coolant ( advised to get concentrated antifreeze and not the ready mixed) as concentrated is stronger.

- advised to start using 10w 40 engine oil and not 5w 30 as thicker oil is better for older engine and it will stop the timing chain rattling. I don’t know how accurate that is ?

- but I have also noted a leak underneath my car by the drivers side allow~ which could be coolant I can send pictures. So I’m not sure where I should start first. Should I get the leaks fixed first and try flushing the cooling system . Before doing timing chain and water pump ?

- he also advised me to add white vinegar or radiator flush to the coolant reservoir and leave cap off and rev engine to 2000 rpm for 2 mins. Did that this afternoon myself

Overall is there any value in doing any repairs with this high mileage. Cars value is approx £1000-£1500.