Vorgelat is the most prone to cracking, (preceded by yellowing) in part due to the use of fast hardeners to speed up the moulding process.
Schwaballac was used by DG Grob and early Glasflugel, it is no longer available due to its toxicity when used in manufacture.
LS, Sclecher and Schempp all used Vorgelat ot later Schuffler T35. It rarely last more than 10-15 years.
My DG202 schwaballac is still perfect, no cracking at all and 38 years old, it is VERY hard as well.
Vorgelat is banned here for refinishing.
Read the AN69 in the link, it goes into great detail.