hard starting diesels. . .

a popular topic, this.

the current theory is to not glow, just crank till it starts which works great if we're warmed up and seems to take about 6 seconds in the 38 degree mornings here in oregon. but my new 900CCA group 49 doesn't always want to turn four that long.
all things being equal, how long do we expect to be able to crank a cold 300D. my battery guys says the problem is not enough reserve amps--that's why i cant both glow & start. i'm wondering if the starter/solenoid is going south.

1984 300 turbo diesel, 110K miles, 20/50 multi-grade oil, regular service to this point.

tia, john