If the meter uses a probe with a BNC connector then any manufacturers pH probe with a BNC connector can be used.The BNC connector is universal and is not proprietary to any specific manufacturer.
Other connectors include the DIN connector which is proprietary. Meaning that if you buy a meter from a manufacturer with a DIN connector then you have to buy probes that are compatible from that manufacturer.
The links to the replacement probes from Milwaukee are at a good price. The comparable one from Hanna would be twice as expensive that is assuming that the Milwaukee is using high temp (HT) glass for the indicating bulb. I would have to look at the specs to know.http://shop.hannainst.com/hi1230b-combination-ph-electrode-for-field-applications.html
Considerations for pH electrodes are:
Glass body vs plastic (PEI AKA Ultem)
Gel filled vs. refillable
Single junction vs. double junction
Glass type - general purpose, low temp, high temp or hydrofluoric acid resistance
Connector type - BNC, DIN, Screw type, etc
If you see combination in the description that means that the probe combines both the reference half cell and the indicating half cell in the same body. They are combined. 99.9% including the Milwaukee probe is a combination pH electrode.
Glass body probes transfer heat much faster than plastic. The reference voltage is dependent on temperature of the fill solution. It is relatively marginal effect but when someone states they want minimal drift then that is a consideration if the temperature of the sample is significantly different than the probe (room) temperature. The down side to glass is the increased risk of breakage. It is the reason that portables are supplied with plastic bodies. Benchtops are typically supplied with glass bodies.
Refillable probes allow for the reference electrolyte to be replenished and changed while gel filled ones cannot. As long as the probe has a good offset and slope it can be used indefinitely.
Single junction vs. double junction. This has to do with the reference half cell. Most probes use a silver/silver chloride reference. There is a silver/silver chloride coated wire in the reference cell. In order to generate a voltage the probe has to have silver chloride in a solution around the wire. It is usually a mixture of potassium chloride (KCl) saturated with silver chloride. The only problem is that silver precipitates very easily by sulfides, metals, and tris buffer. The precipitates will clog the junction. To prevent this from happening a second junction is added to the probe. The first junction is a barrier in which behind it is the reference wire plus the AgCl + KCl. Between the outside junction and the inner junction is another fill solution (KCl) that is silver free so precipitation.
Glass type: Most probes are made with general purpose glass. The glass has a specific resistance at ambient temperature. As the temp goes up the resistance goes down. When the resistance goes down the measuring circuit is affected. To overcome this there are other glass types including low temp glass (has low resistance that approaches the resistance of GP glass at low temps) and high temp glass (resistance is higher than GP glass and approaches the resistance of GP glass as the temp is going up).
If you are measuring 150 oF and up then it is recommended to use a probe with HT glass. The rule of thumb for GP glass in constant use is:
At 25 oC (78 oF) a probe will last 1-2 years (based on regular use as in a factory)
At 50 oC a probe will last 6 months to 1 year
At 75 oC (167 oF)a probe will last 3-6 months
At 100 oC a probe will last around 1 month.
A probe with HT glass will last much longer than one with GP glass at elevated temperatures.
Another design consideration is the material that the junction is made of. The junction can be made of porous ceramic, PTFE (Teflon), glass, open junction, PTFE sleeve, etc. What is recommended is based on the application. For a home brewer use the Milwaukee probe is a good option. If you are a brewery then a different probe would be recommended.
Glass body, refillable, HT glass, double junction (ceramic) - Lab probehttp://shop.hannainst.com/hi1043b-refillable-double-junction-ph-electrode.html
Glass body, refillable, GP glass, double junction (PTFE sleeve) - lab probe for winehttp://shop.hannainst.com/hi1048b-ph-electrode-with-cpstm-clogging-prevention-system.html
Even though the HI1048 is using GP glass the sleeve junction is what is of interest. It was made fro the wine market due to the high solids content in wine must and juice. The PTFE sleeve repels the solids and has a high flow rate. The newer versions allow the sleeve to move out place exposing a ground glass junction making it easy to clean.
Just realize that there are many different styles and any of the manufacturers would be happy to help you in selecting a probe. As long as they have decent Sales Reps they should ask about your application and usage in order to provide a good recommendation.
You can always call Milwaukee directly and they will help you with a replacement and where to buy.