I can't comment on the GB38, but I do have a couple of thousand hours on my 3208 TA Cat engines.
Fuel consumption is actually good and getting better as they are just 'broken in'. These are not 'throw away' engines as the misinformed will say. That comment comes from the fact that these engines have cast in block cylinders rather than liners that other engines may have. Speaking as one involved with the
service end of the medium and heavy duty engine business, I have a fair amount of experience with diesels. Our shop is certifies in: Caterpillar, Detroit Desiel, Cummins,
Volvo, Isuzu, Mitsubishi and more. While the engines that use liners will commonly have the liners (along with the pistons, etc.) replaced during an 'inframe'
overhaul this is due to the design of the liners which are softer that the piston rings (this makes for a quick break-in time and lets the engine go into service at full operating parameters relatively quickly) so again, the liners are a wear item and replacement is common and expected.
The cast blocks however are harder than the piston rings and must be 'broken in' according to a schedule (x
rpm for xx minutes, then y
rpm for yy minutes and so forth) which means that the motors cannot be operated at rated rpm until this process is completed which the truckers don't like. However, when the major service is due (a couple of hundred thousand miles or more) the blocks typically do not need reboring and many times the pistons are re-useable with just a ring change). So broken in properly and operated properly, the service costs should be less on the 3208 type engines.
All that said, no diesel engine likes dirty oil or dirty air and will wear quicker without regular scheduled maintenance. The air filter on any diesel should be cleaned or repaced at every
oil change, but many 'do it yourself' boat operators neglect this. There is a reason that the airflilters have the indicators on them on them on the 3208's, just pay attention.