The glass like substance is due to the leaky injector. This is very likely caused by poor workmanship, as you say, when doing the valve clearances.
Injectors are $1000 each, and the cover is about $800, so its important for you to ensure this is the dealers [censored] up. As long as the dealer is the only person to remove the injectors, then that is good. But a dealer will only guarantee their work for 12months or 20000kms. but this problem will only normally show up after that period. Be prepared to get MMAL involved.
If your vehicle has been serviced to the specifications this will help. if it has missed a valve adjustment, then be prepared for a fight, as whilst poor workmanship is the dealers responsibility, getting the work done is the owners
The white smoke may be caused by a crack in the cylinder head where the injector has been badly fitted.
This will be expensive for someone. Hopefully not you.
I have replaced numerous cylinder heads and injectors on 4N15 engines caused by incorrect fitting, luckily all have been serviced elsewhere, some by dealers, where MMAL have assisted in charging the dealer, even though they denied it was their fault, But mainly, sadly some were borne by the owner as the vehicle had had the valves done outside the dealer network, and the independents were not interested in contributing to a repair.
The procedure for refitting injectors is very precise, and i bet no independents have the manuals or have bothered to find out the procedure.
Dealers have no excuse, they have all the info, so this should not happen.
Silver 2020 MR (4N15) Sportsbar, Towbar, EDS