I looked at this company few months ago but decided to pass. Here are some general rebuttals off the top of my head to your points:
1,2 While NOCIL dominates the domestic market for vulcanisation accelerants and inhibitors, the vast proportion of Indian supply is still imported. Lower auto sales may reduce the total amount of rubber chemical used but does not necessarily imply that NOCIL will suffer since the domestic supply of these chemicals is likely to increase. There was a significant supply disruption due to the Chinese pollution crack down, and the company decided not to take advantage of its customers due to this. They further believe that customers now see the value of having a second supplier.
3 I might be wrong, but in one of the concalls management said that crude derivatives form ~15% of the total cost of these chemicals, and that the industry is mature enough to pass these costs to customers with a 3 month lag.
4 It is very likely that the ADD (on PPD?) is going away by July 2019, since it has been continuing for the last 10 years or so. This is further suggested by the the reports released by the Trade Ministry as they have been reducing the scope of ADD in recent times. In a concall I believe management downplayed this saying that Chinese competitors are even undercutting the ADD, and that the worst case hit to operating margins might be 4%(?).
5 The Mafatlal family has amicably decided to unwind their cross holdings and so the ownership of NFIL and NOCIL will now be completely separate. I believe this is why there has been heavy selling these last few months.
My biggest concern was that, assuming management’s forecasts are accurate, their growth for the next 3-5 years is largely fixed. They are already at full capacity utilisation and are planning a significant capex that they believe will be fully utilised in the next 3-5 years. There is enough information to build a simply DCF and model a few scenarios. I found that in all but the most optimistic scenario of full capacity utilisation in the next 3 years the stock was over valued at PE=16. Perhaps at a PE=10 or less it might provide a margin of safety along with a decent upside.