Is Landlord Required To Fix Drafty Window?

I live in Massachusetts. My partner and I moved into a two-bedroom apartment a month ago, and quickly realized that one of the bedrooms, which we use as a home office, has a drafty window that we didn't notice when we toured the apartment. The room with this window gets cold very quickly, a good 15-20ºF colder than the rest of the apartment, sometimes colder if it's been very cold and windy out.

I notified the landlord of the problem and he sent over a maintenance guy to throw some caulk on around the windows, which hadn't been properly caulked beforehand, but this didn't fix the issue since the draft seems to be coming from between the the moving parts of the window (they are side-sliding windows and the draft is between the panels and along the bottom sliding track), which can't be caulked. I got some temporary weatherstrips and tried stopping up the gaps with that, to no avail.

Maintenance guy and landlord both said the only thing to be done is replace the whole window, which landlord outright refuses to do. I've read the relevant Massachusetts law (105CMR410.500 and 501A), but the definition of "in good repair and fit for use" seems vague to me— how cold does it have to get in here before it's considered not fit for use? The definition of "weathertight" according to the law relies on measurements of gaps for different types of windows, but doesn't seem to have a specification that applies to the specific place the draft is coming from in these old side-sliding windows.

Is the landlord within his rights to refuse to replace the window, or should I keep pushing?

(Here is the relevant section of Massachusetts law, if this helps.)

105CMR410.500

Every owner shall maintain the foundation, floors, walls, doors, windows, ceilings, roof, staircases, porches, chimneys, and other structural elements of his dwelling so that the dwelling excludes wind, rain and snow, and is rodent-proof, watertight and free from chronic dampness, weathertight, in good repair and in every way fit for the use intended. Further, he shall maintain every structural element free from holes, cracks, loose plaster, or other defect where such holes, cracks, loose plaster or defect renders the area difficult to keep clean or constitutes an accident hazard or an insect or rodent harborage.

105CMR410.501 A.

A window shall be considered weathertight only if:

(1) all panes of glass are in place, unbroken and properly caulked; and

(2) the window opens and closes fully without excessive effort; and

(3) exterior cracks between the prime window frame and the exterior wall are caulked; and

(4) one of the following conditions is met:(a) a storm window is affixed to the prime window frame, with caulking installed so as to fill exterior cracks between the storm window frame and the prime window frame; or

(b) weatherstripping is applied such that the space between the window sash and the prime window frame is no larger than 1/16 inch at any point on the perimeter of the sash, in the case of double hung windows and 1/32 inch in the case of casement windows; or

(c) the window sash is sufficiently well-fitted such that, without weatherstripping, the space between the window sash and the prime window frame is no larger than 1/16 inch at any point on the perimeter of the sash in the case of double hung windows and 1/32 inch in the case of casement windows.