Well you are doing maintenance by cleaning indoor unit, so it is being serviced.
Also if gas pressure is ok, then cooling is not much compromised with time.
Orient ac especially old ones are great, using them myself.
You should establish some KPI.
Get a room thermometer, measure how much degree it drops in hour.
Then get ac serviced, where indoor unit is removed and cleaned with water. There are parts where tootbrush cant reach. Ac like other electrical products accumulates dirt over time.
Now measure the temp drop. It will be rapid and more than before.
I have ten years old haier, which was great by my standards , but when it got cleaned indoor unit after removing, it is giving unbelivable cooling based on kpi.
So nothing extra ordinary in ur case. Split ac are mature tech n work great with little maintenance but can work much better with extra effort..
Yearly maintenace is around 2500 , if you bring in tech guy to measure gas and do ac service.