I think it all depends on what model of Marlin, and what you mean by 'older'.
The Model 60 was mentioned.
"older" ones, to me, were made between 1960 and 1984/5. The feedramp/ejector system were one cast unit that could lead to the ejector 'nub' breaking off over time, or the feedthroat/ramp assembly splitting. For a while, Marlin had an upgrade kit to use the current ejector wire system, with a better-designed feedthroat/ramp. At the same time, they changed the front sight to be attached to the barrel, instead of part of a single integrated sight/magazine tube clamp design. AND, they introduced the last shot hold open feature to the Model 60.
The only drawback is that the magazine tube capacity shrank from 17 rounds to 14 rounds [thanks Maryland!] around the same time.
So- I would rate the 1984-2000 produced Model 60 as higher than the 1960-84 era ones.
In the Model 39A, Marlin introduced a rebounding hammer in the 1980s, to go with the cross-bolt safety button they installed in the 1970s.
As a result, the hammer spring isn't as adjustable as it used to be, and the rifle doesn't carry/isn't safe in 1/2 cock position.
Furthermore, the wood used after the 1960s seemed to go downhill, in general.
I would rate the pre-1970 Model 39A as better than the newer ones made in the last 50 years.
In the 1894/1895 carbine design, the same rebound hammer/cross-bolt safety concerns emerge in the 1980s changes. The older ones may be better.
No 795s were made before around 1997, and the action is based on the Model 60- just modified for a detachable magazine.
However, in general the consensus is that Marlin quality, overall, declined once Remington took them over [2007], but some say they began to decline after 2000, when H&R took them over [before selling to Remington].
This doesn't mean Marlins made during that era were junk. It just seems that there were a statistically noticeable increase in reported issues with the Marlins made during those eras.
I love Marlins- but would prefer to buy a lever action made in/before the 1970s, and a Model 60 from the 80s.
My Model 60 is a transitional model: replaceable front sight, LSHO and upgraded feedthroat/ejector, but with original 17-round mag tube. Mine was the Model 600 from the mid-80s.