What are the thoughts on using the conditioner Subaru puts in all their engines, in the Rover/GM Aluminum engines. Would this help seal cracked blocks?
Probably, Cadillac had a similar one for there aluminum blocks.
For some reason, Subaru quit carrying this fluid. My local dealer is one of the largest volume dealers in the country, and they are no longer able to source it. I find this somewhat disconcerting, as I purchased a reman engine through NAPA for my sister-in-law's 2002 Outback, and there was the little blue bottle, along with a notice that failure to use the fluid would void her 3 year unlimited mile warranty.
I could find no explanation from Subaru regarding the fluid.
K-Seal will seal corroded heads leaking head gaskets weeping core plugs and I dare say cracked blocks.
https://www.kseal.com/
It seals so well that it will even try to seal the drain tap when you change the coolant. Last time I drained the previous RV8, which had weeping core plugs at the back of the block, I had to remove the whole drain tap from the rad before I could get the coolant out, and it wasn't a rusted relic, it was a new tap !
Ivor
I think Amazon still sells the Subaru "conditioner".
Amazon still sells this. I had a Subaru WRX and always used the conditioner except for one time when I had the timing belt replaced by a shop that said they would use the conditioner but actually used a generic sealer. About 3 months later I noticed the first signs of a head gasket leak and I immediately put in two containers of "conditioner". Problem was solved instantly and I drove the car for another year before finally selling it (240,000 miles). I use it routinely in all my older cars as insurance. It has never caused any problems.
I've had good luck with K-Seal
Jim